DD asked me about this the other day. She has been curious about it ever since her little sister was born. She asks a lot about how I became her mommy, which I usually explain by saying "because you came out of my belly." But, now she wants even more info, specifically about DH being her daddy, etc. I don't remember exactly how she phrased it. I was able to put off the subject, but I want to be more prepared the next time she asks.
I always think telling her the truth is best, but I want to do it in a way that doesn't freak her out and/or give her something to talk about in school (only for the other parents to come running to me!).