From Time Magazine:
I'm not a big fan of young kids having Facebook.
I have to say, I agree. Mrs. Obama doesn't allow her children - aged 9 and 12 - to have Facebook. I think it's too dangerous out there. A kid should be prohibited at least until they are old enough to drive (if not 18).
Children are annoying. They also need to be protected. They make stupid decisions and lack good judgment (I say this as someone who was a kid who made stupid decisions and lacked good judgment). Keeping pre-teens off Facebook is a smart way to help protect your children.