I'll add the suggestion that when discussing body parts... use the real words. When your kids find out you've been truthful with them on this matter, then they will trust you more on the topics where their safey (e.g., drugs) and the safety of their future (e.g., pregnancy, stds) is concerned.

I was stunned when I found out in sex-ed class that penis and vagina were not my parents' equivalent of the weenie, dick, hoohoo, and a variety euphonisms my friends were taught by their parents. It gave me new respect for my parents AND their trust in me.