Many parents of children who suffer from autism suspect something may be wrong with their child by the age of 18 months and generally seek medical help when the kid is 2 years old. Typical difficulties noticed in autistic children:

There are cases when children seem to be normal before the age of 1 - 2 years and suddenly regress comes. Children start losing social and language skills they have learnt. This is regressive autism.
People suffering from autism may often:     

In fact, the signs differ from moderate to very severe.

Communication difficulties generally include:

Interaction with other people:

Reaction to sensory information: