I can only tell you what we do in my home. Most of my grandkids have facebook acocunts. I don't allow anyone to friend them that I don't personally know or a friend personally knows, like my best friends mom is friends with the kids so they can be neighbors in the games, she lives in another state but I trust my friend to know her mom and say if she's safe to friend the kids or not. I made their ages much older than they are but kept the original day and month. The computer is in the living room with a picture of Christ above the monitor along with some Gary Olsen prints. They are never on the computer, even just playing games, without me or my husband in the living room. While they are on facebook they are on playing farmville, farmtown and cafe world with relatives, friends, and siblings that live in other homes. I selected on the privacy settings that only friends can see information about them and I left everything blank, no personal information at all, my choices for network were one of 2 large cities in my state and both are hundreds of miles away. When you enter their name in your search you get a page up with a gray screen that says "XXX only shares information with people they know" "Would you like to send a friend request?". I have about a third my 157 friends that have their kids on too. Only some of them are friends with my grand kids. They don't need to be friends with my friends from high school, although they are good upstanding people, most are Baptist preachers or work for the Baptist General Convention.
I feel it is an honest to goodness personal choice for you. If they have computers in their room they are already going places you don't know about. We have had talks at church about how to manage kids on the internet and I feel secure in our choices, hence the central location of the computer and pictures of Christ above the monitor. You have to have that peace of mind too. You won't sleep easy if you don't have that confidence.
I am on facebook a lot and have never had issues, some people try to friend me but if I don't know them I just "ignore" them and they can't ask again. I enjoy getting reaquainted with my local friends, relatives, high school friends, and people at my church that have moved away. I really like Facebook and the security features it offers.
Lots of the people I interact with have children and they have accounts, the kids have pictures of themselves in their photo albums, they post about their football games, activities, etc...that give too much information to my way of thinking but again they are only posting to a certain group of people. I have also found a lot of people put pictures of their pets, their kids, and cartoon characters as their profile picture, so a stranger really can't tell if you're an adult or a kid if they did see the picture.