Astrid, my mother is the same.. she gets so annoyed when she's see some kind of kids show or one with kids in it, like in Kindergarten Cop), where they refer to the whole of the female genitals as the vagina..

Logan calls his penis, a penis.. For a while he would point to his nipples and say "Apples" I guess it sounds the same. He calls my breasts "Booboos", even though I tell him they're breasts. He walked around the other day with bowls on his chest saying "Look at my booboos Mummy!"
When he comes in the shower he points to my "bits" and says "Where Mummy penis?", but I don't know what to call them so I just say that Logan is a boy so he has a penis and Mummy is a girl and doesn't have a penis. But I think I like Astrids idea of calling it a fanny.. just have to hope he doesn't watch The Nanny and get confused like I did the first time I heard the part about her being thrown out on her fanny! I didn't know at the time in the US they called a bum a fanny.