If you suspect your child of being autistic, you will need to get them to see a specialist as in a paediatrician, there can be different signs depending on the age of the child. The earliest this is diagnosed the better the outcome for the child.
It their first year they may not be interested in other people, nor will they make eye contact or smile like other babies do.
As toddlers, those with ASD might not respond to their name. They might focus on one or 2 activities repetitively, like lining up toys. They may not be interested in playing with other children. They might develop unusual ways of speaking.
Older children with ASD might have difficulties in social situations, following instructions or making friends.
There are what is regarded as behavioural red flags such as
The child often has marked repetitive movements, such as hand-shaking or flapping, prolonged rocking or spinning of objects
Many children develop an obsessive interest in certain toys or objects while ignoring other things
The child may have extreme resistance to change in routines and/or their environment
The child may be resistant to solid foods or may not accept a variety of foods in their diet
There are often difficulties with toilet training
The child may have sleeping problems
The child may be extremely distressed by certain noises and/or busy public places such as shopping centres
Jo-AnneRamplings 
Dearest Jo-Anne,
That are a lot of things to consider and to further investigate.
Good thing that there now is more known and it can be traced and treated.
Hugs,
Mariette
Yes we have come a long way in our treatment of people with this condition
AMEN!
You are so rigjt. The earlier the better.
Yes it is
If in doubt – it’s best to find out.
Linda xx
That’s for sure