Children with ASD display a delay in the understanding and use of language. Often, parents grow concerned when their child does not respond to language; the communication difficulty is often mistakenly thought to be hearing loss. Children with ASD are less likely to point to objects with their index finger; rather, they often communicate their needs by taking an adult by their hand and leading them to the item that they want. Many children with ASD develop speech, however they are likely to have difficulty with grammatical structure and the social use of language. Also, children appear to have difficulties with the auditory processing of language. There are many children with ASD who develop fluent speech, social understanding and communication.

Children with ASD are often perceived as isolating themselves from the rest of the world, in fact they will often avoid and resist physical contact. Children frequently display limited eye contact and joint attention skills, and they are less likely to respond to their name being called than a typical child. Children with ASD rarely display an interest in the activities of their siblings or other children. Some parents report that it is as though other children do not exist and that their child will walk straight into the path of another child without any acknowledgement. Older children with ASD appear to find it difficult to understand the perspective of another person and to interpret social cues such as facial expression and body language. This inability results in difficulties with responding to the subtleties of social interaction.

Children with ASD generally display behaviours that are repetitive, extreme, and limited in imagination. Children will engage in such behaviours as hand flapping, lining up objects, spinning items, turning switches on and off, rewinding videos to watch the same clip over and over again. Children with ASD frequently display delays in toy and imaginative play skills, rather than play functionally with a toy they tend to arrange them into patterns. Children with ASD are frequently upset by changes in routine and often display an inability to be flexible with regard to food, dressing and outside activities. Many children have extreme tantrums which result in aggression towards their caregivers or themselves. Children are able to develop skills that increase a more socially appropriate behaviour repertoire.