http://www.prevent-abuse-now.com/stats.htm...m#Substantiated
The information is available on official .gov sites as well, but it's been a while since i actually went looking for it, and it's surprisingly difficult to find the information. But basically, 1.5 percent of children up to the age of 3 are sexually abused, according to that site, which quotes . In these cases, the offender is usually a parent.
And these are obviously situations where the perp has to be caught in the act, or a doctor has to notice signs of abuse or something, 'cause obviously the victim can't talk about it, so nobody really knows just how many children up to the age of 3 have been abused.
I've seen other surveys of girls in high school, that had results showing 1 in 5 girls had been sexually abused at some stage in their life. Says something about the number of unreported cases of child abuse. I think it was 1 in 8 for boys.
But the only official statistics i can find right now are for actual reported cases of child abuse, and they show at least 1.5% of chlidren are abused.