What's a good age to start that talk with your kids?

I think a good age to talk to it is around ten years old, because that's about when girls body starts to change and they get curious, is most likely when you explain it in detail. And probely dicuss it brefly when they ask "where do babies come from."

When they ask questions.

It is a good idea to start talking about their bodies and their "parts" when they are young, but not in a sexual way, just the basic "this is your vagina, this is your penis, pee pee comes out of there, it's your private place." stuff like that.

If you start talking when they are young you'll build the trust that you will need when they become teens. If they know that they can ask you anything and get a correct and accurate response, then they will continue coming to you with their questions. Let them dictate how much info to give and when to give it, there is not set age.

Good Luck.

And if you read posts on here you will see where kids often at 12 believe they are grown and already are very sexually active. Not all by any means but some. So keep this in mind that at 12 they will be in school with others that are sexually active all ready.

I would start the basics of bodily functions early on as just matter of fact. Young children have a natural curiosity about their bodies. These days, girls in particular, are often finding changes happening at an earlier age than in years past. I have had a few girls in my class who started their periods at 9, one was totally unprepared and quite frightened. Keep things age appropriate... simple answers without a lecture. If you happen to find what we call "teachable moments", where a situation presents itself, for example on a television show, that leads into a natural conversation on a topic, even better.