M.,
I am assuming that you work at a preschool, because if you worked at a school aged public school, you would know what to do: you would be required to make a referral for an evaluation, the school then has the obligation to evaluate, even if they have to override the parents lack of consent, which can be done in Due process hearing. The school has an affirmative obligation to do so if they take federal funds.
Schools often discourage teachers from making such referrals, because the do not want to identify children, and schools often will play along with parents who take this kind of attitude to save money, even though they know what is going on. This does not bennefit children, so please do not play along, document what you are seeing (objectivley) for the good of the child. By objectively, I mean to write down what he did, when he did it, what happened before he did it, and so on, without any kind of comentary about why, what he was thinking, what you thought he was trying to accomplish, etc. Johnny picked up a crayon, there was a fire truck siren from outside, Johnny colored on the walls...Not Johnny grabbed the crayon from the box because he did not want Sarah to have it and when he heard the noise from the street he went crazy and colored on the walls to get my attention)
After you have collected data over several days, give the information to the parent and make a referral to the local school distisct because once the child is 3, they are included in the public schools obligation for "Child Find" under IDEA, which means that they are responsible for finding all the children in thier boarders with disablities and offering a Free and Appropriate Education (FAPE).
Schools try to keep teachers from "suggesting" what they think the problem is because once you have brought up a specific diagnosis, they are obligated to evaluate for that even if the psycholgist thinks that they do not need to. They must evaluate when a disabilty is "suspected" and by bringing up the diagnosis, you raise suspecion that they must then act on.
Something to remember, once you have met one child with Autism, you have met one child with Autism, and that is all you can really say. They are all very different, and the behaviors that you see from them are shared by a whole constelation of diagnisis; ADHD, Tourette, Bipolar, dyslexia, etc, will all share some symptoms in common. Focus isntead on what you see that is atypcial (NOT ABNORMAL) and document it so that the parent can use this to thier advantage (meaning that they can get appropriate services as early as possible) from the public school, this knife cuts both ways, if you have documented approriately, you have a way to deal with the parent who is in denial too and by all means, if the child has behavior that is so disruptive that he can no longer participate in your program, you need this kind of documentation so that the parent has their first dose of reality, I hope that you do such a good job that it is thier last dose and they realize that their son needs help.
M. (educational advocate for kids with disablities)