I am pretty forward with these kinds of quesions with my friends. I don't have too many adult people that I'm friends with whom I haven't asked about their childhood sexual experiences.
And I know it is only anecdotal but only a few of them have had actual sex as prepubescents. By "actual" I mean penetration sex (either oral, anal or vaginal). Lots of them tried but didn't know it was supposed to actually go in, so they didn't get much past humping.

I often wonder what the real figures would be.
When I think about that kid in the UK who is a father at 13. Sheesh... he's so darn cute! The thought of him having sex to orgasm.... don't go there Cat!!! :S

My son (now 19) was telling me the other day that his school friends at 14 were telling him that they'd been hooking up sexually with girls since they were in primary school because it was "cool". That sure wasn't how it was in my day. I was a cute boy, looking for sex and I couldn't find many other boys (or girls) who wanted to play along and believe me I tried.

Blessings
Cat.