As it stands, the Facebook terms of service dictate that members be at least 13 years old to set up an account. However, a recent indicates that as many as 7.5 million Facebook users are under 13, and two-thirds of those kids are under 10. Either they, or their parents, simply lied about their age to set up the account.
And, why not? Facebook is an awesome platform for kids to stay in touch with friends, grandparents, or cousins that live across the country. Sure, there are a myriad of other ways--email, instant messaging, video chat, etc.--to accomplish the same thing, but Facebook is different. Rather than having to initiate one on one communication, Facebook lets kids simply share what is going on in their lives so that friends and relatives can all be connected and involved.
Zuckerberg seemed to imply that the Children's Online Privacy Protection Act () is preventing Facebook from allowing children to join, and suggested that Facebook might one day take on the challenge of altering or repealing that legislation to change the rules. But, COPPA doesn't prevent Facebook from allowing children to join, it just requires a little extra effort from Facebook.
COPPA puts protections in place that require a site operator to obtain verifiable parental consent before collecting, using, or disclosing any personal information related to the child. It doesn't ban such activity. It just means that Facebook would have to make a reasonable effort to ensure that a parent or guardian is aware that the child is joining Facebook, and that the parent or guardian grants permission for information to be collected and shared.
I know that other sites manage to do this because I have had to give my permission time and again for my kids to join sites like Neopets, or Club Penguin, or Wizard101. All Facebook has to do is add a step that sends a consent verification email to a parent or guardian when someone under 13 sets up an account. What's the big deal?