Of course, they would then ask again. Then he would reply: BIG BOY!
(Well, big boys are stinky, so they use deodorant, probably not their mother's though...)
And sometimes he is, a big boy that is. For example if he has an potty accident it's because he chooses to, not because he doesn't know how to do it right (which is small consolation in the moment).
But sometimes he is a "small boy." That's when he either a) doesn't want to do things that big boys do (participate in scripture reading, use the potty, come when he's called), or b) can't do the things that big boys do (go to school, reach high things, mow the lawn, etc.) So when he announces to us that "I a small boy" it is either with defiance, or sorrow.
Two. It's a confusing age.