I don't really like this word labelling, I had some experience of autism when I was teaching, and there is a huge resistance to actually diagnosing autism in young children, even with Health Visitors and other health professionals. Anya is correct, the sooner it is diagnosed, the sooner strategies can be put into place to support the child and family. We should be aware that autism has a large spectrum, with very mildly affected people to severely affected people. It very well may be that he's just very shy with adults, and based on my own experience that sounds likely, but I'm not a doctor, autism is only ever diagnosed by a pediatrician, and so if his parents are concerned they may wish to speak to their GP to organise an assessment. Don't sorry about people saying you're labelling him, you're expressing a concern and only a pediatrician can diagnose him.