In a Times article about the word, "Va-jay-jay", apparently popularized on "Oprah" and "Grey's Anatomy" (neither of which I watch):

"Technically speaking, the vagina is the canal that leads from the uterus to the outside of the body, a fact that has led both Ms. Ensler [Eve Ensler, of Vagina Monologues fame] and Ms. Steinem [you really ought to know who that is ] to write that vagina — while not a word that should be stigmatized — is inadequate because it is not inclusive enough. It does not, they have pointed out, include the labia and clitoris, the nerve-rich locus of a woman’s sexual pleasure. 'I’m hoping that the use of this new word is part of the objection to only saying vagina since it doesn’t include all of women’s genitalia, for instance the clitoris, in the way that vulva does,' Ms. Steinem said."

This has been my point all along, people! The area that is usually being referred to is NOT (just) a vagina! And I for one didn't really want my 3 year old saying vulva all the time. So we have a nickname for the area. But my daughter knows she has a vagina. She knows she has a clitoris, a urethra, labia, etc. etc. We just opt to call the whole area something kind of cute and funny.

Which brings me to "balls". My son knows there is a scrotal sac with testicles, etc. etc. But they LOOK like balls! I think "dick" is probably inappropriate slang, but is balls bad? I got in trouble with a neighbor over this one. So we've switched to "marbles" for the interim. Equally funny, but won't have lasting power as he grows.