Becca also cries easily, often because she is frustrated or upset that she can't communicate her needs. I was worried about it when she started school but have found her classmates to be very empathetic and protective of her when she has a hard time. Younger kids are so intuitive about what the other kids are feeling and if reminded on how they would feel in the same situation are usually very quick to take care of another's feelings. Hopefully he will have some of the same kids in his class every year so that when they get older and cattier they will already be close to him and not take part in any of the cruel behavior that kids seem to pick up along the way
Will your triplets all be in the same class? Or does your son know anyone in his new class (I believe you mentioned they were moving from a private pre-school to a public kindergarten?) If not, maybe you can meet up with some of the kids from his new class during the summer so he can get to know them a little bit better so the change won't be as overwhelming.
Also--is he going to summer school as part of his IEP? That could help get him used to the new environment before the regular school year begins. Or maybe they will let him sit in on a session before the school year ends so he sees how fun it is and spends the summer looking forward to the new start.
Make sure the teachers and/or aides are aware of how anxious he gets (it's likely included in your IEP but make sure they know the extent of things) and let them know signs to look out for that might tip them off that he might be getting upset. They might be able to separate him from an upsetting situation before the other kids realize anything is wrong.
If I think of anything else I'll post it--these were just the things that popped in my head when I saw your post. It's so hard starting them in a new environment and not being able to be there to help if needed--
--Sara