Even before babies can wrap their tongues around their language they use everything else available to them to tell their parents how they are feeling and what they need. For children with Autism however, communication and social interaction do not come easily, nor are they necessarily desired.
Autism also heads a more common and specific group referred to as Autistic Spectrum Disorders, labelled as such because Autism and similar disorders can vary in degree and type across individuals. This means that although the diagnostic label may be the same, one child may exhibit most of the possible symptoms where another child will only exhibit a few, and one child may experience severe symptoms where another child may experience much milder versions. This is why Autism is often defined as either a low-functioning type (many symptoms or severe effects) or a high-functioning type (few symptoms or mild effects).
It should be noted though as well that some children with Autism may still demonstrate nonverbal gestures and attempt to engage with the environment. Some autistic children may also be talented in specific areas where language is not required, such as mathematics or music.