M.S.
Skip the children's potty and get a seat the goes over top the toilet seat. It fits over nicely and there is nothing to clean up (except the little cup that catches pee splatter) They are probably sold in the same area of the store as the pottys. This will also help him to adjust to using the real toilet (which will prove very helpful when you are in a store later and he has to go and there is no little potty!)