Important info on Taxes please help.?

ok for starters my son is 7 months old he was born in october. my inlaws have put him on their taxes sense they were buying his diapers for abut 3 months or so. now the money they reseived from their taxes does that go to me or them. i have people telling me that is my money because Mathew is my son and then i have people telling met hat it's theirs because they were buying diapers for he first 3 months. but thats only about $300 and they got back 1,500 just for my boy. so please help. thanks.