I agree with what everyone has said, but I also think it wouldn't hurt to mention it to your son's carers. Feedback like that is important, and can be easily incorporated into the program, such as role playing and discussing how what we say can affect others feelings etc etc And they should do it in a global approach to the class, a way that doesn't single out your DS. That way they may also watch a little closer to see the interactions he is having with the older children and see just what is going on/being said and give you some more feedback also.

I am a firm believer in really keeping the communication flowing between families and carers, as it helps so much to ensure everyone is more settled and happy as it can be really easy for things to blow out quickly.