Children suffering from autism spectrum disorder are affected in three ways. 

All of them have communication problem with their parents and 
  people around them. 

They not interested in contact with the outside world or any social milieu,

They are engrossed in doing repetitive behavior for hours. 

Problems in communication are one of the key symptoms of autistic children. Autistic children talks very less throughout their lives. Even this level of communication varies with each child. Some children remain mute for life. Others may be extreme slow in picking up language skills as late as 5 or 6 years of age. They may speak using only a word or two to form a sentence, or be monosyllabic. At times they may simply repeat the words that are being said to them. 
Autistic children finds it difficult to understand the cues of the conversation, the nuances of how the communication bounces back to and fro from a set of participants.

Repetitive behavior is also an integral part of the world of autistic children. As children they may spend hours in lining up cars or objects, or being engrossed in a particular type of behavior involving any object. They get upset if anyone disturbs their work, accidentally or otherwise. Their world moves in a set pattern and anything that disturbs the pattern upset them. Even their daily routines need to be followed in exactly the same manner everyday of their lives.

Some other symptoms of autistic children can be mental retardation, seizures, fragile x chromosomes, and tuberous sclerosis or formation of benign tumors on some organs like brain etc.