I don't know. What HAS happened to our world? It's unacceptable, sure, but they're kids. I was doing some inappropriate stuff while chasing girls around the playground when I was in the fourth grade. That was 34 years ago. We can't assume what's going on at home. Something has to be done, sure, but what? I'm not sure.
It might be worth noting sexual activity amongst children is not new. It's pretty much always gone on to some degree or another. Some infants masturbate, for example.
Most just don't want to think or talk about it.
Of course, not trying to suggest sexual activity should be tolerated in school. I'm not sure what I'm saying. It's a tough subject, and I don't really know what to say about it.