Dd9 knows about sex, and periods, and babies. We have also taught her that sex is for grown ups, and it is not something that you do until you are a grown up yourself.
This is why it bothers me so very much when I see young kids encouraged to dress, act, and do things that have traditionally been for teens.
Kids think - hey I can dress like an adult, see R rated movies, wear makeup, high heels, have my own cellphone, hang out at the mall by myself, buy my own clothes and CDs, go to concerts -- I'm not a "kid". Having sex is just another cool thing that I can do.
It sickens me when I see girls my daughters age dressed like little adults (and skanky little adults to boot). It doesn't surprise me a bit that two 13 year olds are pregnant - we have totally obscured the line between childhood and adulthood.