Anecdotal evidence suggests that it's not unusual for children to have Facebook accounts. You even hear of parents setting up the occasional account for an infant. But it seems Facebook does try to enforce its terms of service and keep kids off the site, with one exec indicating it boots 20,000 youngsters a day.
As for that interesting statistic, it comes from former FTC Commissioner Mozelle Thompson (who's now an advisor to Facebook). According to Australia's Daily Telegraph, he told the Australian Federal Parliament's cyber safety committee, "Facebook removes 20,000 people a day, people who are underage."
Which adds up to about 7 million accounts per year.
That's done in at least in part to protect the children. After all, there's zero chance of kids encountering bullies, objectionable material, or sleazy adults on Facebook if they're made to stay clear of the site.
It also helps safeguard Facebook. Consider all the negative press that might result from any sort of tragedy, followed by additional scrutiny from lawmakers and perhaps calls to boycott the social network.
So we might see more of an effort from Facebook to regulate who's able to sign up, considering that Thompson admitted the current system often doesn't work. Australian authorities are thinking about ways to educate parents and lawmakers, as well.