I bet a dollar my 9 year old nephew could rattle off the names of more STDs than I can. And up until his sex ed class he still thought it was for peeing. A wee bit early, I think.
If someone is going to teach it that young it should bloody well be the parents. Because that is a BIG call.
By 9 I'm assuming that you are talking about fourth grade. It needs to be taught this early. Girls can get their first period around then. Sexual activities start in fifth grade (or whenever kids in your area get in Middle school which is 5th here). The more "chaste" sex related games (kissing spin the bottle) start then, and by seventh and eighth grade, a significant amount of people are playing far less innocent sex related games/activities (oral sex spin the bottle, handjobs, etc). Kids have sex (vaginal, oral, etc) when they are in middle school, and many of them do not know how to do it safely. There needs to be education to scare them away from it. Maybe not in fourth, but somewhere between fourth and sixth. In fourth, they need to know the basic anatomy parts (especially the girls).
Most people don't realize how young these activities are being performed.