There aren't any 'adult' names for genitals. There are anatomically correct terms (vulva, penis, labia etc), twee pet names (foof, nooni, twinkle etc), accepted slang (willy, fanny etc), crude names (twat, pussy, cunt, gash etc) and incorrect labels.
'Let children be children' has nothing to do with it.
We operate on the policy that things have a name, pure and simple and we use that name. If a nickname grows up alongside it, then that's an organic thing, just like you have strange nicknames for lots of things. I will not pass onto my children a legacy of their genitals being something they need to alternatively name or risk shame for saying the name out loud. All this faux cringing and 'oh I couldn't possibly say vulva out loud', just reinforces the ridiculous attitude we have towards the female genitals. It's no wonder that calling somebody a cunt or a twat is highly offensive, but you call them a dick or a penis and it's just a bit light-hearted.
Fear of the name only increases fear of the thing itself.
I don't really care what other people use as a descriptor but all these accusations of 'adult names' and forcing children to grow up and let children be children and proper names are crude is absolutely unnecessary.