ugh.. no idea here. My 4 year old hates wearing underwear too. He almost never wears them. He tells me they hurt "the little balls in his pee pee" heheh. I've tried boxers, bigger sizes, having him pick the underwear out himself. nothing works. If I force him to wear them in the morning, I find a little pair of undies hiding somewhere a couple hours later. Maybe they'll grow out of it??