Well, thankfully I don't have to deal with this yet. But I have a friend (who is a midwife) with an almost 3-year-old whose ambition in life is to be a mommy. The problem is, her kid's a boy. So she explains to him that because he's a boy, someday he's going to be a daddy, not a mommy. And he answers that it's true, right now he has a *****, but when he grows up, he's going to have a yoni so that he can be a mommy.
And Nexa, "yoni" is actually quite a good answer to the question of what to call female genitalia, since it's neither exclusionary (***** only really covers external genitalia and ****** only covers internal) nor derogatory (there are no names for female genitalia that are nether clinical nor vulgar) nor sexist (the origins of the word "******" means sheath of scabbard for a "sword" wink wink nudge nudge.)
"
Yoni" is catching on, at least among crunchy types, because it's a very positive, almost reverent term that encompasses the whole of female genitalia.