Diana Lang; Nick Cone; Laura Overstreet; Stephanie Loalada; Julie Lazzara; Jessica Traylor; and Jamie Skow
Early childhood is a time of pretending, blending fact and fiction, and learning to think of the world using language. Young children move away from needing to touch, feel, and hear about the world toward learning basic principles about how the world works, they hold some pretty interesting initial ideas. For example, a three-year-old child might worry about whether or not they will go down the drain with the water in the bathtub. A child might protest if told that something will happen “tomorrow” but be willing to accept an explanation that an event will occur “today after we sleep.” Concepts such as tomorrow, time, size, fact, fiction, and distance are all tasks typically part of cognitive development during the preschool years.
Piaget’s Second Stage: The Preoperational Stage
Young children enjoy pretending to “play school.” (Image Source: Maxpixel, CC0)
Piaget’s second stage of cognitive development following the sensorimotor stage is called the preoperationalstage and typically coincides with ages 2-7. The word operation refers to the use of logical rules, so sometimes this stage is misinterpreted as implying that children are illogical. While it is true that children at the beginning of the preoperational stage tend to answer questions intuitively as opposed to logically, children in this stage are learning to use language and how to think about the world symbolically. These advances in symbolic thought help build foundations for future stages.
Piaget believed that we are continuously trying to maintain balance in how we understand the world. With rapid increases in motor skill and language development, young children are constantly encountering new experiences, objects, and words. When faced with something new, a child may either assimilate (bringing in new information) it into an existing schema by matching it with something they already know or expand their knowledge structure to accommodate (change the new learning) the new situation. During the preoperational stage, many of the child’s existing schemas will be challenged, expanded, and rearranged. Their whole view of the world may shift.
Pretend Play
Pretend play is typically a favorite activity at this time. For a child in the preoperational stage, a toy has qualities beyond the way it was designed to function and can now be used to stand for a character or object unlike anything originally intended. A laundry basket, for example, can be a boat or flip it over to be the shell of a turtle or hermit crab!
Piaget believed that children’s pretend play and experimentation helped them solidify the new schemas they were developing cognitively. This involves both assimilation and accommodation, which results in changes in their conceptions or thoughts for future logical operations.
Egocentrism
Egocentrism in early childhood refers to the tendency of young children to think that everyone shares the same feelings, knowledge, and views of the world. Piaget’s classic experiment on egocentrism involved showing children a three-dimensional model of a mountain and asking them to describe what a doll that is looking at the mountain from a different angle might see. Children tend to choose a picture that represents their own, rather than the doll’s view. Children tend to display an inability to take on another person’s point of view and perspective. However, when children are speaking to others, they tend to use different sentence structures and vocabulary when addressing a younger child or an older adult.
Video Examples
The children in this interview display egocentrism by believing that the researcher sees the same thing as they do, even after switching positions.
Similar to preoperational children’s egocentric thinking is their structuring of cause-and-effect relationships based on their limited view of the world. Piaget coined the term “precausalthinking” to describe the way in which preoperational children use their own existing ideas or views, like in egocentrism, to explain cause-and-effect relationships. Three main concepts of causality, as displayed by children in the preoperational stage, include animism, artificialism, and transductive reasoning.
Animism is the belief that inanimate objects are capable of actions and have lifelike qualities. An example could be a child believing that the sidewalk was mad and made them fall down, or that the stars twinkle in the sky because they are happy. To an imaginative child, the cup may be alive, the chair that falls down and hits the child’s ankle is mean, and the toys need to stay home because they are tired. They may believe that stuffed animals and objects have feelings just as they do. Young children do seem to think that objects that move may be alive, but after age three, they seldom refer to objects as being alive (Berk, 2007). Many children’s stories and movies capitalize on animistic thinking. Do you remember some of the classic stories that make use of the idea of objects being alive and engaging in lifelike actions?
The story of the Velveteen Rabbit exhibits animism for the stuffed animal to come alive. (Image Source: Alyssa Miller on Flickr, CC BY)
Artificialism refers to the belief that environmental characteristics can be attributed to human actions or interventions. For example, a child might say that it is windy outside because someone is blowing very hard, or the clouds are white because someone painted them that color.
Finally, precausal thinking is categorized by transductive reasoning. Transductivereasoning is when a child fails to understand the true relationships between cause and effect. Unlike deductive or inductive reasoning (general to specific, or specific to general), transductive reasoning refers to when a child reasons from specific to specific, drawing a relationship between two separate events that are otherwise unrelated. For example, if a child hears a dog bark and then a balloon pop, the child would conclude that because the dog barked, the balloon popped.
Cognition Errors
Between about the ages of four and seven, children tend to become very curious and ask many questions, beginning the use of primitive reasoning. There is an increase in curiosity in the interest of reasoning and wanting to know why things are the way they are. Piaget called it the “intuitive substage” because children realize they have a vast amount of knowledge, but they are unaware of how they acquired it.
Centration and conservation are characteristic of preoperative thought. Centration is the act of focusing all attention on one characteristic or dimension of a situation while disregarding all others. An example of centration is a child focusing on the number of pieces of cake that each person has, regardless of the size of the pieces. Centration is one of the reasons that young children have difficulty understanding the concept of conservation. Conservation is the awareness that altering a substance’s appearance does not change its basic properties. Children at this stage are unaware of conservation and exhibit centration. Imagine a 2-year-old and 4-year-old eating lunch. The 4-year-old has a whole peanut butter and jelly sandwich. He notices, however, that his younger sister’s sandwich is cut in half and protests, “She has more!” He is exhibiting centration by focusing on the number of pieces, which results in a conservation error.
A demonstration of the conservation of liquid. Does pouring liquid in a tall, narrow container make it have more?
In Piaget’s famous conservation task, a child is presented with two identical beakers containing the same amount of liquid. The child usually notes that the beakers do contain the same amount of liquid. When one of the beakers is poured into a taller and thinner container, children who are younger than seven or eight years old typically say that the two beakers no longer contain the same amount of liquid, and that the taller container holds the larger quantity (centration), without taking into consideration the fact that both beakers were previously noted to contain the same amount of liquid.
Irreversibility is also demonstrated during this stage and is closely related to the ideas of centration and conservation. Irreversibility refers to the young child’s difficulty mentally reversing a sequence of events. In the beaker situation, the child does not realize that, if the liquid was poured back into the original beaker, then the same amount of liquid would exist.
Centration, conservation errors, and irreversibility are indications that young children are reliant on visual representations. Another example of children’s reliance on visual representations is their misunderstanding of “less than” or “more than”. When two rows containing equal amounts of blocks are placed in front of a child with one row spread farther apart than the other, the child will think that the row spread farther contains more blocks. When something takes up more space it is seen as having more.
Video Example
This clip shows how younger children struggle with the concept of conservation and demonstrate irreversibility.
Class inclusion refers to a kind of conceptual thinking that children in the preoperational stage cannot yet grasp. Children’s inability to focus on two aspects of a situation at once (centration) inhibits them from understanding the principle that one category or class can contain several different subcategories or classes. Preoperational children also have difficulty understanding that an object can be classified in more than one way. For example, a four-year-old girl may be shown a picture of eight dogs and three cats. The girl knows what cats and dogs are, and she is aware that they are both animals. However, when asked, “Are there more dogs or more animals?” she is likely to answer “more dogs.” This is due to her difficulty focusing on the two subclasses and the larger class all at the same time. She may have been able to view the dogs as dogs or animals, but struggled when trying to classify them as both, simultaneously. Similar to this is a concept relating to intuitive thought, known as “transitive inference.”
Transitive inference is using previous knowledge to determine the missing piece, using basic logic. Children in the preoperational stage lack this logic. An example of transitive inference would be when a child is presented with the information “A” is greater than “B” and “B” is greater than “C.” The young child may have difficulty understanding that “A” is also greater than “C” unless clearly defined.
As the child’s vocabulary improves and more schemes are developed, they are more able to think logically, demonstrate an understanding of conservation, and classify objects.
Was Piaget Right?
It certainly seems that children in the preoperational stage make the mistakes in logic that Piaget suggests that they will make. That said, it is important to remember that there is variability in terms of the ages at which children reach and exit each stage. Further, there is some evidence that children can be taught to think in more logical ways far before the end of the preoperational period. For example, as soon as a child can reliably count, they may be able to learn conservation of number. For many children, this is around age five. More complex conservation tasks, however, may not be mastered until closer to the end of the stage around age seven.
Theory of Mind
How do we come to understand how our mind works? The theory of mind is the understanding that the mind holds people’s beliefs, desires, emotions, and intentions. One component of this is understanding that the mind can be tricked or that the mind is not always accurate.
A two-year-old child does not understand very much about how their mind works. They learn through imitation, they start to understand that people do not always agree on things they like, and they have a basic understanding of cause and effect (although they often fall prey to transitive reasoning). By the time a child is four, their theory of the mind allows them to understand that people think differently, have different preferences, and even mask their true feelings by putting on a different face that differs from how they truly feel inside.
To think about what this might look like in the real world, imagine showing a three-year-old child a bandaid box and asking the child what is in the box. Chances are, the child will reply, “bandaids.” Now imagine that you open the box and pour out crayons. If you now ask the child what they thought was in the box before it was opened, they may respond, “crayons.” If you ask what a friend would have thought was in the box, the response would still be “crayons.” Why?
Before about four years of age, a child does not recognize that the mind can hold ideas that are not accurate, so this three-year-old changes their response once shown that the box contains crayons. The child’s response can also be explained in terms of egocentrism and irreversibility. The child’s response is based on their current view rather than seeing the situation from another person’s perspective (egocentrism) or thinking about how they arrived at their conclusion (irreversibility). At around age four, the child would likely reply, “bandaids” when asked after seeing the crayons because by this age a child is beginning to understand that thoughts and realities do not always match.
Theory of Mind and Social Intelligence
This awareness of the existence of mind is part of social intelligence and the ability to recognize that others can think differently about situations. It helps us to be self-conscious or aware that others can think of us in different ways, and it helps us to be able to be understanding or empathic toward others. This developing social intelligence helps us to anticipate and predict the actions of others. The awareness of the mental states of others is important for communication and social skills. A child who demonstrates this skill is able to anticipate the needs of others.
Autism and Impaired Theory of Mind
People with autism or an autism spectrum disorder (ASD) typically show an impaired ability to recognize other people’s minds. Autism is characterized by persistent deficits in social communication and interaction across multiple contexts, as well as restricted, repetitive patterns of behavior, interests, or activities. Children with this disorder typically show signs of significant disturbances in three main areas: (a) deficits in social interaction, (b) deficits in communication, and (c) repetitive patterns of behavior or interests. These disturbances tend to be present in early childhood, typically before age three, and may lead to clinically significant functional impairment. Symptoms may include lack of social or emotional reciprocity, stereotyped and repetitive use of language or idiosyncratic language, and persistent preoccupation with unusual objects.
About half of parents of children with ASD notice their child’s unique behaviors by age 18 months, and about four-fifths notice by age 24 months, but often a diagnoses comes later, and individual cases vary significantly. Typical early signs of autism include:
No babbling by 12 months.
No gesturing (pointing, waving, etc.) by 12 months.
No single words by 16 months.
No two-word (spontaneous, not just echolalic) phrases by 24 months.
Loss of any language or social skills, at any age.
Communication deficits can range from a complete lack of speech to one-word responses (e.g., saying “Yes” or “No” when replying to questions or statements that require additional elaboration), to echoed speech (e.g., parroting what another person says, either immediately or several hours or even days later), to difficulty maintaining a conversation because of an inability to reciprocate others’ comments. These deficits can also include problems in using and understanding nonverbal cues (e.g., facial expressions, gestures, and postures) that facilitate normal communication.
Repetitive patterns of behavior or interests can be exhibited in a number of ways. The child might engage in stereotyped, repetitive movements (rocking, head-banging, or repeatedly dropping an object and then picking it up), or she might show great distress at small changes in routine or the environment. For example, the child might throw a temper tantrum if an object is not in its proper place or if a regularly- scheduled activity is rescheduled. In some cases, the person with an autism spectrum disorder might show highly restricted and fixated interests that appear to be abnormal in their intensity. For instance, the child might learn and memorize every detail about something even though doing so serves no apparent purpose. Importantly, autism spectrum disorder is not the same thing as intellectual disability, although these two conditions can occur together.
The qualifier “spectrum” in autism spectrum disorder is used to indicate that individuals with the disorder can show a range, or spectrum, of symptoms that vary in their magnitude and severity: Some severe, others less severe. Some individuals with an autism spectrum disorder, particularly those with better language and intellectual skills, can live and work independently as adults. However, most do not because the symptoms remain sufficient to cause serious impairment in many realms of life.[1]
Causes of Autism
Estimates indicate that nearly 1 in 88 children in the United States has autism spectrum disorder; the disorder is 5 times more common in boys (1 out of 54) than girls (1 out of 252).[2] The exact causes of autism spectrum disorder remain unknown despite massive research efforts over the last two decades.[3] Autism appears to be strongly influenced by genetics, as identical twins show concordance rates of 60%–90%, whereas concordance rates for fraternal twins and siblings are 5%–10%.[4] Many different genes and gene mutations have been implicated in autism.[5] Among the genes involved are those important in the formation of synaptic circuits that facilitate communication between different areas of the brain (Gauthier et al., 2011). A number of environmental factors are also thought to be associated with increased risk for autism spectrum disorder, at least in part, because they contribute to new mutations. These factors include exposure to pollutants, such as plant emissions and mercury, urban versus rural residence, and vitamin D deficiency.[6]
There is no scientific evidence that a link exists between autism and vaccinations.[7] Indeed, a recent study compared the vaccination histories of 256 children with autism spectrum disorder with that of 752 control children across three time periods during their first 2 years of life (birth to 3 months, birth to 7 months, and birth to 2 years).[8] At the time of the study, the children were between 6 and 13 years old, and their prior vaccination records were obtained. Because vaccines contain immunogens (substances that fight infections), the investigators examined medical records to see how many immunogens children received to determine if those children who received more immunogens were at greater risk for developing autism spectrum disorder. The results of this study clearly demonstrated that the number of immunogens from vaccines received during the first 2 years of life was not at all related to the development of autism spectrum disorder.
Language Development
Reading to young children helps them develop language skills by hearing and using new vocabulary words.
A child’s vocabulary expands between the ages of two to six from about 200 words to over 10,000 words through a process called fast-mapping. Words are easily learned by making connections between new words and concepts already known. The parts of speech that are learned depend on the language and what is emphasized. Children speaking verb-friendly languages such as Chinese and Japanese tend to learn verbs more readily, but those learning less verb-friendly languages such as English seem to need assistance in grammar to master the use of verbs.[9] Children are also very creative in creating their own words to use as labels such as a “take-care-of” when referring to John, the character on the cartoon Garfield, who takes care of the cat.
Children can repeat words and phrases after having heard them only once or twice, but they do not always understand the meaning of the words or phrases. Figures of speech and expressions are often taken literally instead of figuratively. For example, two preschool-aged girls began to laugh loudly while listening to a tape-recording of Disney’s “Sleeping Beauty” when the narrator reports, “Prince Phillip lost his head!” They imagine his head popping off and rolling down the hill as he runs and searches for it. Or a classroom full of preschoolers hears the teacher say, “Wow! That was a piece of cake!” The children began asking “Cake? Where is my cake? I want cake!”
Overregularization
Children learn the rules of grammar as they learn the language. Some of these rules are not taught explicitly, and others are. Often when learning language intuitively children apply rules inappropriately at first. But even after successfully navigating the rule for a while, at times, explicitly teaching a child a grammar rule may cause them to make mistakes they had previously not been making. For instance, two- to three-year-old children may say “I goed there” or “I doed that” as they understand intuitively that adding “ed” to a word makes it mean “something I did in the past.” As the child hears the correct grammar rule applied by the people around them, they correctly begin to say “I went there” and “I did that.” It would seem that the child has solidly learned the grammar rule, but it is actually common for the developing child to revert back to their original mistake. This happens as they overregulate the rule. This can happen because they intuitively discover the rule and overgeneralize it or because they are explicitly taught to add “ed” to the end of a word to indicate past tense in school. A child who had previously produced correct sentences may start to form incorrect sentences such as, “I goed there. I doed that.” These children are able to quickly re-learn the correct exceptions to the -ed rule.
Vygotsky and Language Development
Lev Vygotsky hypothesized that children had a zone of proximal development (ZPD). The ZPD is the range of material that a child is ready to learn if proper support and guidance are given from either a peer who understands the material or by an adult. We can see the benefit of this sort of guidance when we think about the acquisition of language. Children can be assisted in learning language by others who listen attentively, model more accurate pronunciations and encourage elaboration. For example, if the child exclaims, “I’m goed there!” then the adult responds, “You went there?”
Children may be hard-wired for language development, as Noam Chomsky suggested in his theory of universal grammar, but active participation is also important for language development. The process of scaffolding is one in which the guide provides needed assistance to the child as a new skill is learned. Repeating what a child has said, but in a grammatically correct way, is scaffolding for a child who is struggling with the rules of language production. Scaffolding is a process of integrating new information to solve problems and adapt to the environment.
Private Speech
When you are struggling with a problem, trying to remember something, or feel very emotional about a situation, we may talk to ourselves. Children talk to themselves too. Piaget interpreted this as egocentric speech, or speech engaged in because of a child’s inability to see things from other points of view. Vygotsky, however, believed that children talk to themselves in order to solve problems or clarify thoughts. As children learn to think in words, they do so aloud before eventually closing their lips and engaging in private speech or inner speech. Thinking out loud eventually becomes thought accompanied by internal speech, and talking to oneself becomes a practice only engaged in when we are trying to learn something or remember something, etc. This inner speech is not as elaborate as the speech we use when communicating with others.[10]
30 Million Word Gap
To accomplish the tremendous rate of word learning that needs to occur during early childhood, it is important that children are learning new words each day. Research by Betty Hart and Todd Risley in the late 1990s and early 2000s indicated that children from less advantaged backgrounds tend to be exposed to millions of fewer words in their first three years of life than children who come from more privileged socioeconomic backgrounds. In their research, families were classified by socioeconomic status (SES), into “high” (professional), “middle” (working class), and “low” (welfare) SES. They found that the average child in a professional family hears 2,153 words per waking hour, the average child in a working-class family hears 1,251 words per hour, and an average child in a welfare family only 616 words per hour. Extrapolating, they stated that, “in four years, an average child in a professional family would accumulate experience with almost 45 million words, an average child in a working-class family 26 million words, and an average child in a welfare family 13 million words.” The line of thinking following their study is that children from more affluent households would enter school knowing more words, which would give them advantage in school.
Hart and Risley’s research has been criticized by scholars. Critics theorize that the language and achievement gaps are not a result of the number of words a child is exposed to, but rather alternative theories suggest it could reflect the disconnect of linguistic practices between home and school. Thus, judging academic success and linguistic capabilities from socioeconomic status may ignore bigger societal issues. A recent replication of Hart and Risley’s study with found that the “word gap” may be closer to 5 million words, not the oft-cited 30 million words previously proposed. The ongoing word gap research is evidence of the importance of language development in early childhood.
What do you think about this “word gap” notion?
Psychodynamic and Psychosocial Theories of Early Childhood
Freud’s Psychodynamic Theory
Consistent with the sexual development we learned about in the health section, Freud asserted that children pass through two stages of his theory during early childhood: stage 2 (anal stage) and stage 3 (phallic stage).
The anal stage begins around 18 months of age and lasts until the child is three years old. During the anal stage, Freud believed that the libido source shifted from the mouth (in stage 1) to the anus. The child, then, receives pleasure from defecating. The child, at this point, understands that they have some amount of control over their lives, including control of when and where they defecate. This can lead to difficulties during potty training. What matters, in terms of Freud’s theory, is how the parent reacts to inevitable difficulties in potty training. Parental reactions during potty training may set-up their child to react in one of two ways: (1) parents who are harsh or who ridicule the child for mistakes may have children who stubbornly hold on to their feces in an effort to not have an accident – these children may become anal retentive or (2) parents who are too easy going may have a child who reacts by purposefully making a mess – these children may become anal expulsive. Adults who are anal retentive tend to be stubborn, very neat, rigid, and stingy. Adults who are anal expulsive tend to be messy, wasteful, and harsh.
The phallic stage of psychosexual development occurs from ages three to six. According to Freud, during the phallic stage, the child develops an attraction to the opposite sex parent, which is called the Oedipus Complex for boys and the Electra Complex for girls. When the child recognizes that the opposite sex parent is unavailable, the child learns to model their own behavior after the same-sex parent. The child develops their own sense of masculinity or femininity from this resolution.
Erikson’s Psychosocial Theory: Initiative vs. Guilt
While Erik Erikson was influenced by Freud, he believed that the relationships that people have, not psychosexual stages, are what influence personality development. At the beginning of early childhood, the child is still in the autonomy versus shame and doubt stage (stage 2).
By age three, the child begins stage 3: initiative versus guilt. The trust and autonomy of previous stages develop into a desire to take initiative or to think of ideas and initiate action. Children are curious at this age and start to ask questions so that they can learn about the world. Parents should try to answer those questions without making the child feel like a burden or implying that the child’s question is not worth asking.
These children are also beginning to use their imagination. Children may want to build a fort with the cushions from the living room couch, open a lemonade stand in the driveway, or make a zoo with their stuffed animals and issue tickets to those who want to come. Children are more assertive in social interactions and activities. Another way that children may express autonomy is in wanting to get themselves ready for bed without any assistance. To reinforce taking initiative, caregivers should offer praise for the child’s efforts and avoid being overly critical of messes or mistakes. Soggy washrags and toothpaste left in the sink pale in comparison to the smiling face of a five-year-old emerging from the bathroom with clean teeth and pajamas!
That said, it is important that caregivers do their best to kindly guide the child to the right actions. Remember that according to Freud and Kohlberg, children are developing a sense of morality during this time. Erikson agrees. If the child does leave those soggy washrags in the sink, have the child help clean them up. It is possible that the child will not be happy with helping to clean, and the child may even become aggressive or angry, but it is important to remember that children are still learning how to navigate their world. They are trying to build a sense of autonomy, and they may not react well when they are asked to do something that they had not planned. Parents should be aware of this, and try to be understanding, but also firm. The use of gentle parenting, positive discipline, and related consequence will help guide children to positive behaviors. Guilt for a situation where a child did not do their best allows a child to understand their responsibilities and helps the child learn to exercise self-control (remember the marshmallow test). The goal is to find a balance between initiative and guilt, not a free-for-all where the parent allows the child to do anything they want to. Caregivers must guide children if they are to have a successful resolution in this stage.
Video Example
Movies, television, and media, in general, provide many examples of psychosocial development. The movie clips in this video demonstrate Erikson’s third stage of development, initiative versus guilt. What other examples can you think of to demonstrate young children developing a sense of autonomy?
Three types she labeled as non-social (unoccupied, solitary, and onlooker) and three types were categorized as social play (parallel, associative, and cooperative). Younger children engage in non-social play more than those older; by age five associative and cooperative play are the most common forms of play.[11]
The development of play is an important milestone in early childhood. Play holds a crucial role in providing a safe, caring, protective, confidential, and containing space where children can recreate themselves and their experiences through an exploratory process.[12][13] Freud, Vygotsky, and Piaget all viewed play as providing positive outcomes for children.
Further, Parten[14] observed 2 to 5-year-old children and noted six types of play. During this stage, pretend play allows children to express their thoughts, emotions, fears, and anxieties. Early childhood play can be understood by observing the elements of fantasy, organization, and comfort. Fantasy, the process of make-believe, is an essential behavior the child engages in during pretend play; organization helps the child to structure pretend play into a story and to utilize cause-and-effect thinking; and comfort is used to assess the ease and pleasure in the engagement in play.[15]
As children progress through the stage of early childhood, they also progress through several stages of non-social and social play. Stages of play is a theory and classification of participation in play developed by Mildred Parten Newhall in 1929.[16] Parten observed American children at free play. She recognized six different types of play:
Parten’s Classification of Types of Play in Preschool Children[17]
Unoccupied Play
Children’s behavior seems more random and without a specific goal. This is the least common form of play.
Solitary Play
Children play by themselves, do not interact with others, nor are they engaging in similar activities as the children around them.
Onlooker Play
Children are observing other children playing. They may comment on the activities and even make suggestions, but will not directly join the play.
Parallel Play
Children play alongside each other, using similar toys, but do not directly act with each other.
Associative Play
Children will interact with each other and share toys, but are not working toward a common goal.
Cooperative Play
Children are interacting to achieve a common goal. Children may take on different tasks to reach that goal.
American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders, 5th edition (DSM-V). Washington, DC: Author. ↵
Centers for Disease Control and Prevention. (2012). Prevalence of autism spectrum disorders, autism and developmental disabilities monitoring network, 14 sites, United States, 2008. Morbidity and Mortality Weekly Report: Surveillance Summaries, 61(3), 1–19. http://www.cdc.gov/mmwr/pdf/ss/ss6103.pdf↵
Meek, S. E., Lemery-Chalfant, K., Jahromi, L. D., & Valiente, C. (2013). A review of gene-environment correlations and their implications for autism: A conceptual model. Psychological Review, 120, 497–521. ↵
Autism Genome Project Consortium. (2007). Mapping autism risk loci using genetic linkage and chromosomal rearrangements. Nature Genetics, 39, 319–328. ↵
Meek, S. E., Lemery-Chalfant, K., Jahromi, L. D., & Valiente, C. (2013). A review of gene-environment correlations and their implications for autism: A conceptual model. Psychological Review, 120, 497–521. ↵
Kimmel, M. S. (2008). The gendered society (3rd ed.). Oxford: Oxford University Press. Kinney, D. K., Barch, D. H., Chayka, B., Napoleon, S., & Munir, K. M. (2009). Environmental risk factors for autism: Do they help or cause de novo genetic mutations that contribute to the disorder? Medical Hypotheses, 74, 102–106. ↵
Hughes, V. (2007). Mercury rising. Nature Medicine, 13, 896-897. ↵
DeStefano, F., Price, C. S., & Weintraub, E. S. (2013). Increasing exposures to antibody-stimulating proteins and polysaccharides in vaccines is not associated with risk of autism. The Journal of Pediatrics, 163, 561–567. ↵
Imai, M., Li, L., Haryu, E., Hirsh-Pasek, K., Golinkoff, R. M., & Shigematsu, J. (2008). Novel noun and verb learning in Chinese, English, and Japanese children: Universality and language-specificity in novel noun and verb learning. Child Development, 79, 979-1000. ↵
Vygotsky, L. S. (1962). Thought and language. Cambridge: M.I.T. Press, Massachusetts Institute of Technology. ↵
Dyer, S., & Moneta, G. B. (2006). Frequency of parallel, associative, and cooperative play in British children of different socio-economic status. Social Behavior and Personality, 34(5), 587-592. ↵
Winnicott, D. W. (2016). Why children play. Oxford University Press. ↵
Erikson, E. H. (1963). Childhood and society (2nd Ed.). New York: Norton. ↵
Parten, M. B. (1932). Social participation among pre-school children. The Journal of Abnormal and Social Psychology, 27(3), 243–269. https://doi.org/10.1037/h0074524↵
Salcuni Silvia, Di Riso Daniela, Mabilia Diana, Lis Adriana (2017). "Psychotherapy with a 3-Year-Old Child: The Role of Play in the Unfolding Process". Frontiers in Psychology. Retrieved from https://www.frontiersin.org/articles...016.02021/full↵
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