I too have taught the girls the proper names, vagina and penis.
We've also taught Nina that her vagina is not a toy, and that unless she permits it, no-one is to touch it. If she is ever feeling sore on her vagina, she will always ask for me. She'll even say to dh, 'no daddy, I would like mummy to look at my vagina'. He has always respected that, and I think he'd prefer that as well LOL.