At seven I didn't know what sex was either. But I knew that something was wrong when a little boy in my class used every chance he got to stick his hand, hard and painfully, into my crotch. (This was back in the days when little girls wore dresses and white socks to school.) I couldn't concentrate in school because it seemed as though every time I turned my back or focused on my work he was there, crawling around on the floor under my desk and laughing maniacally. It was horrible. I was too embarrassed to tell anyone for awhile, but finally the teachers noticed. He didn't get suspended, just chewed out. That didn't do much good; he broke some of my school projects in revenge. I now realize he must have endured some kind of sexually-based torment at home to turn into such a psycho by age seven, but the fact remains that he made me miserable and that kids can sexually harass each other at a very young age.
Yeah, next when 1 one and half year old boy baby kisses a one and half year old girl baby, the little guy will end up on a sex offender list.
As for the article the little girl grabbed his pee pee and he grabbed hers in retaliation.
Kids that age have no notion of sex whatsoever. Boys and girls don't even want to have anything to do with each other until their twelve at the earliest.
We used to have an expression for it when I was young, "Girls Fleas!!!!"