The social networking site kicks off around 20,000 underage users per day, its chief privacy adviser, Mozelle Thompson, told Australia's parliament this week.
He admitted that the site's way of weeding out those who don't meet the 13-and-up age requirement -- essentially a user-entry honor system -- is "not perfect," because there's no mechanism for detecting kids who simply enter a false age.
"There are people who lie. There are people who are under 13," Thompson said.
A recent Pew study found that nearly half of all U.S. 12-year-olds use social networking sites -- and privacy concerns in regard to Facebook's younger members have been growing of late. This month, Sen. Al Franken, a Minnesota Democrat, wrote to Facebook CEO Mark Zuckerberg (pictured) to argue for reforms in the site's privacy measures. "Under Facebook's policy, 13 million users under the age of 18 may be allowed to share their personal information just like adult users," Franken wrote. "These younger users are the most vulnerable to predators on Facebook and the rest of the Internet and it should be impossible for them to inadvertently share their phone numbers and home addresses with anyone."
But Franken's figures don't factor in the unknown number of Facebook users under 13.
Other sites that are popular with kids handle the issue in differing ways. MySpace also requires users to be at least 13, but like Facebook, it has no practical way to verify that information. Disney.com allows children 12 and under to surf the site, and collects some personal information from them before they're eligible to participate in competitions, for example. Yahoo! doesn't allow kids 12 and under to register without the consent of a parent. Like Disney, it collects some limited idenifying information for participation in competitions and similar interactive features.