Truthfully, the jury is still out on whether social media is good for any of us, but at least as adults we should have some sense of responsibility and judgment for what we put out there and what we share with whom. I say "should" knowing full-well that isn't always the case. After all, I do peruse my FB feed and am frequently appalled by what I find there. Do people not realize that their drunken posts may impact their ability to get/keep a job? Apparently not. But they are adults and it is their decision to put this info out there.
For children and teens, social media poses a whole different set of issues. While an adult should have that sense of judgment, young people are still developing it. We were all there once. Would you want every mistake you made as a teen forever preserved on the internet for the world to see? Would you want every insult someone ever sent your way forever in print - a bullying that never goes away? Or conversely, a cruel word you sent someone else's way lingering long after you had regretted the incident? Would you want your most embarrassing moments videotaped and shared for the whole world to see (or at least what seems like the whole world). Would you want the world to know your boyfriend/girlfriend dumped you by changing their "relationship status" before you even did. Add to this the volatile rush of teen hormones and emotion, and social media is a social minefield. There is never a down moment. Everything is there for everyone to see and comment on.
FB states that users should be 13, although many children younger than that are on it (I know several.) And FB wants to lower the age requirement. I admit, I've let my kids play supervised games on my FB account, but there is no way I'd let them get an account as pre-teens. Thankfully, they don't want one. Honestly, I dread the day that they do.
Every generation has to deal with new and different issues raising children. Internet use and social media is perhaps the defining issue of ours. Newsweek recently ran an insightful article on the issues inherent with allowing children access to social media: The Perils of Parenting in the Digital Age. It's definitely worth reading.