My son is 20 months old and I have started potty training him. He has been interested in the toilet for a month or two. He will pee and poop whenever I sit him on there, but still won't let me know when he goes when he isn't on the toilet. I let him either run naked or put his big boy underwear on, but he stil won't let me know when he's soiled himself. What do I do to help him tell me? He will say "pee pee" after he goes in the toilet so I know he knows he's going...