Keep That Up and You'll Go Blind

A little while back The Boy discovered his Yoo Hoo - aka penis. Since that fateful day, whenever the mood strikes him, he yanks on it in the bath.

I'm non-plussed. Should I stop him, or let him explore? I mean, to be honest one day he'll succumb to his hormones and do that anyways, so maybe I'm getting worked up for no reason.

I know there's nothing sexual about what he's doing, but it still weirds me out.