Take her to your pediatrician and voice your concerns to them. They will run a battery of tests on her to find out if she is developmentally delayed or not. They can also refer you to the appropriate medical doctors or counselors to help you out with this issue.
Has anyone called child protective services on this mother yet? If these children are in danger, then the need to be protected by whomever knows of this situation. This needs to be you protecting them. These children can also try to speak with counselors at their schools and the school system should be able to do something for them.
I agree with specialmom on this. He isn't harming anyone and he isn't harming himself so just let him be. If this were my son, I'd want him to have a way of out letting his excitement.
I think that for your piece of mind, I would take your son to see a doctor and have him tested, the worst that could happen is the tests come back negative for everything and your son turn out to be fine. Make a list of things that are going on with him and have the teachers do the same and then show these lists to the doctor and go from there. Good Luck.