It has nothing to do with the Internet, this is a case of poor parenting. You can't just let your kids go, pay no attention to what they're doing and expect the schools and the Internet to educate them, parents have to be intimately involved in their children's lives.
My kids have had their own computers since they were 4 and Internet access since they were 7-8. The trick is, my wife and I are involved in their lives, we know what's going on, we know, in general terms, what they're doing and they know there are rules and consequences for violating those rules. I can't say they've always been perfect, my oldest daughter, for instance, is an artist and she got a DeviantArt account before she turned 13 by creating a fake e-mail account for my wife to give them permission to give her an account. She got caught and she got punished, had she just come to us in the first place, we would have given her the account anyhow. She learned her lesson. It's easier to just come to us and talk to us than to reap the consequences of not doing so.