first the problem is that if u ask ur son where his rebbe is during recess it is most likly not with the class! so thats half the problem!
secound if was gonna say what many said have him bring a ball and ull see plenty will play with him but make sure he knows the rules of the games the boys r playing it is possible they r not letting him play cuz they fell he dont know how and will just ruin there game hazolcha