My 3 yr old niece loves being naked. Anytime she has a bath at my parents place, as soon as she's dry she runs around the house and sticks out her bum for everyone to give her a little smack then she squeals and giggles and runs to the next person and it goes on and on until someone else decides it's time for her to get dressed. Apparently the other night she was hot so stripped off to her undies and refused to put anything else on except her new boots (she's such a girl and LOVES shoes). A friends daughter who is a similar age does the same thing, runs around the house and yard naked when she can. I think it's just one of those 'kid things'