Say WHAT!?

So, we are blessed with an extremely smart oldest child. All of our kids are bright, but from the time she was very young, sweet Lulu has been a smart little booger. Since learning to read a few years ago her world has opened up to the point that I feel like I should be reading the encyclopedia at night to keep up with her!
One of the things I love about Lulu is that she loves to read the Bible. In the mornings she uses a book light to read once she's awake while her sisters are still snoozing away. Just about any time she gets a free moment in her room she's reading the Word. It's so encouraging to see her relaxed up on her top bunk just reading away.
Last night she was reading while we were doing bath night and all of the sudden I heard the words I've been dreading since the day she took her first breath, "Mom. What is...sex? Yeah, S-E-X. That's SEX, right? What is SEX?" I seriously almost peed my darn pants! Manly was just about passed out in the bathroom floor covered in conditioner. I said, "Well. Where did you see that word?" "In this verse." she says. She goes on to read it to me. "Leviticus 18:9 'Do not have sex with your sister. It does not matter whether she is your father's daughter or your mother's daughter. It does not matter whether she was born in the same home as you were or somewhere else.' So is SEX the same as adultery?" I looked to Manly who was at this point lying in the fetal position.
I don't think she's quite ready for the full REAL answer, so I told her that there were a lot of things that were reserved for a husband and wife only and that sex was one of those things. I said, "I'll tell you more about it when you are closer to getting married age, but for now I think that's about all you need to know."
SO, now we are bracing ourselves for the next step...YIKES!! Passport to Purity here I come!