My two year old keeps getting zits on his butt. We thought it was his diapers so we changed them. But he just keeps getting them. Any advice?

See answer. Best to see his pediatrician to get a definitive diagnosis as maybe it is (especially at this hot time of the year) a type of heat rash, and a steroid cream may help, as well as keeping the area dry. It could be a contact dermatitis if his diaper is wet or full, etc. There are also a very common skin conditions such as milia that usually occur on the face, but can occur on the butt. Best wishes.