Agree that letting anyone go doesn't solve anything really. Many times we have said that when it comes down to it that parents will do what is best for them and not worry about us and there are times when we need to worry about us and not them. If the mom pulls then fine to a certain extent as she was somewhat temporary anyways and this is a good time of year to replace if you are going and by sept the three should have pretty much grown out of the phase. Is the child that is older in their face a little too much, bigger than they are so towers above when they play as in do they feel he presents some sort of danger. Does he like that the others get in trouble? Does he like the attention he gets when he gets bit? Does he respond to warnings of stay away from XXX or you may get bit - ie make him responsible for keeping himself safe.