Despite how Facebook is filled with underage children, Mark Zuckerberg recently addressed the issue at the NewSchools Summit where Zuckerberg revealed that he wants to grant younger children access to Facebook.

CNN Money reports that Facebook founder Mark Zuckerberg
spoke about children under 13 years-old on Facebook while attending a
recent NewSchools Summit in California. Despite the current Facebook
age restriction of 13-years and older, Zuckerberg stated that he wants
Facebook open to younger people.
"In the future, software and technology will enable people to learn a
lot from their fellow students," said Zuckerberg. "That will be a fight
we take on at some point. My philosophy is that for education you need
to start at a really, really young age."