Yes if the autistic child is happy they will laugh and smile when they feel like laughing and smiling.
I've known a few autistic children that would not laugh or smile when around strangers but when they were at home or around people they knew they would easily laugh and smile.
It depends on the child but me autistic children to laugh and smile and are otherwise normal aside from a few other things.
Some children may be autistic and you may not even realize it from the outside unless you know the child.
Some behavioral signs of autism include inappropriate social interaction, poor eye contact, compulsive behavior, impulsivity, repetitive movements, self-harm, or persistent repetition of words or actions.
Developmental signs of autism are learning disability or speech delay in a child.
Cognitive signs of autism are intense interest in a limited number of things or problem paying attention.
Other signs of autism are unaware of others' emotions or depression as well as anxiety, change in voice, sensitivity to sound, or tic.
Some kids may have a less severe form of autism and may be normal in other ways but if they have poor eye contact then it can mean the child is either just shy or has autism.