Hello!
I've a 4 year old son with high functioning Autism. With Aspergers and High Functioning cases, it can sometimes be quite hard to tell until the child is older or if you pay a professional to do it.
I suspected my son had Autism when he was around 18 months but KKH doc keep telling me he's ok. At around 3, I got him checked out by a child psychologist (friend's sis) who was kind enough to spend half a day observing him at home and she confirmed my suspicions.
There are a few things you can try out (but NOT all kids with Autism will show the signs).
An Autistuc child would be likely to do the following (NOT NECESSARILY ALL AUTISTIC CHILDREN THOUGH)
*Look at your finger instead of the object if you pointed at something and asked him to look at it.
*Wave "Bye Bye" with his palm faceing himself.
*Skipped crawling stage.
My kid had delayed speech and was very particular in the way things should be done. Unconsolable tantrums was another sign for me - the only way a tantrum stopped was when he fell asleep crying. Also, he taught himself how to recognise numbers and alphabets before he was 20 months (my husband and I are the most laid back people when it comes to hothousing our children, so no-way he picked it up from home, neither was my son placed in any childcare facilities that could have taught him that). He was (and still is) also totally OBSSESSED with Thomas and Friends. He would know if anyone shifts his displays even by half a cm - not kidding!
If you suspect your kid has Autism, get him checked and sent for therapy ASAP - early intervention is the best thing you can do (I regret ignoring my initial motherly instinct and listening to docs who keep telling me that my son is ok!). KKH does testing for Autism and theraphy too but the waiting time is crazy. Private centres cost more but you get help faster. Also, the records will not appear anywhere - so can choose not to declare the child's Autism status if you don't want to mark him for life.
Another thing is to buy all the insurance for the child in question BEFORE getting him tested. As far as I know, no company would insure an Autistic person.
Just to clarify, am not a professional in the area, but am willing to share what info I have with anyone who might need help. Just PM me.