I think when a child is curious about body parts, we should help them learn as much as they want to about them -- be it the vulva or the foot.
But, I think the proper nomenclature debate is a little over the top. If you go to the doctor and say "my vagina hurts", he or she is going to ask you a series of questions to find out exactly what you mean. Same as if you go to the doctor and say "my stomach hurts" or "my chest hurts" or "my hand hurts". Each of these is made up of many parts and elements that could be causing the pain. I mean, really...it is useful to have a solid understanding of human anatomy, but I don't think it is such a huge issue that we must always and only use the appropriate scientific and specific term for each body part.