I agree with kinkypixie. You always need a variety of words to describe anything, especially if you're referring to it repeatedly. It's a good thing there are so many words for our various organs.
And, P'Gell, what kinds of books are you reading? Seriously. I appreciate the word "va-jayjay," but can't stand the word "hoo-ha", so I commiserate with you. Sexual repression pisses me off too. HOWEVER, I will say that words like that, which you ascribe to childish use have their place. (All words have their place.) It may not be your kink, but I think they'd go very well in age-play literature. Espcially infantalistic age-play literature. (And "ba-doink-adoink" is a noun, not a verb. It's MAKE ba-doink-adoink.)
What I particularly despise is medical jargon in my erotica. No, it's not his penis, it's his cock. Or his tool. Or his rod. It's not my vagina. It's my pussy, my cunt, my slit, my whore hole. Then again, if it were a medical scene, medical names may be appropriate.
I think it also bears mentioning that "cock" and "pussy" refer to barnyard animals. We often forget that the degradation of slang has class implications.