I've tried. Really, I did. I've started, and stopped, and started again, and all I have left to say is this:
You can keep your kids away from the Internet. You can tell them they can't go on Facebook until they are 14, watch every Twitter they make and every blog post you write, but you know, it doesn't matter.
It doesn't matter because one day, some kid is going to take a picture of your 12 year old and post it on Facebook with some less then kind comments. All that work to keep them safe and protected and away from the social crap that happens isn't going to matter anymore.
Because even though you've kept them away from it, everyone else has seen it. And then what your child doesn't know, hurts them after all.