I found a great article on the latest changes to Facebook's privacy settings. It gives clear advice to parents on how to keep their kids' Facebook world safe. If Facebook continues to periodically change the way their service operates, then parents need to check their kids' settings frequently. (At present, it seems, Facebook changes about once a week, much to the frustration of their users. I think the guy who had the idea for "New Coke" in the 80's is running things there.)
Please read the article then sit down with your kids and double-check to make sure that their profile is only being seen by those they know. It may be a good time to have a more detailed conversation about keeping their identity safe online. If you get on a roll and the subject of why "sexting" can literally ruin their lives (jail time anyone?), then more power to you.