A.G.
Well what it sounds like is the baby tooth fell out and you can see the top of the new permanent tooth coming through. Remember baby teeth are short and little so it could look like only half of his tooth when really it was the whole baby tooth. Because teeth are somewhat hallow on the inside for the roots if it broke clear in half you would be able to see inside the part that's still in his mouth and it would probably be causing a lot of pain for him to have it exposed like that. Look again and see if it just looks like maybe the top of a permanent tooth.