J.
I have a 4 yr old boy and a 2 yr old daughter and so we have discussions about penises and vaginas a lot. I give them the correct names and try to treat it as 'everyday' words so that they won't feel that it is something to be ashamed or embarressed about. We talk about who has penises and who has vaginas. If you start this kind of talk right away and give them correct terminology they will feel more comfortable talking with you about their questions and not try to "shock" people in public by using the words. Howevever, I know it may at first be hard and embarissing to talk about these matters, I think by starting young it will be easier to discuss puberty, sex and birth control when they are teenagers! Good Luck!