I think I'd put both of them in time out at the same time. Your son might need some "quiet time" to be reminded that his behavior is not acceptable and maybe the little yorkie can use the same. By removing both of them from the scene and making both understand that this is the action that will be taken EVERY time...hopefully over time it will get better. I understand that you love both...but the next bite could land on your childs face and that could be really bad....for everyone involved.
