One thing we need to make sure we talk to our kids about is God's gift of sex. I don't hope to unpack the whole topic here, but hopefully give a few starters.
One of the easiest ways to start is just talking about babies. My wife and I are expecting so the topic comes up with my older three boys somewhat frequently. Do we engage their questions or do we shut them down? Sex isn't anything to be ashamed of when it's in a marriage relationship, so how do we communicate the truth to children while protecting their innocence as much as possible.
(I say "as much as possible" because kids will lose their innocence at some point. We all do. I'd rather be the one giving them the truth about difficult things then someone random breaking it on them all at once in a junior high locker room.)
So what do you talk about? To start, just ask their thoughts on where babies come from. After hearing them out, step up and explain it to them. For young kids they can just know that moms and dads make babies together. As a child grows, however, they need to hear that you make a baby by having sex. They need to hear the names of the body parts involved. And they need to know that within a marriage God says its good.
There's a start on this big topic. More to come sometime.