Earlier quoted context omitted.
Sadly, I think you're going to have to ban them. COPPA[1] makes it risky to have children under 13 on your web site without clear parental consent. ..you could let them send in a note from their parents to get unbanned :-) 1. http://en.wikipedia.org/wiki/Childrens_Online_Privacy_Protec...
If the First Amendment allows children to traffic in snuff films, Nazi regalia, bomb making manuals, Satanist tracts, classified nuclear information, and so forth while in a government school , it's safe to assume that COPPA is an unconstitutional prior restraint on free speech. I am astonished that the ACLU has not already handed the FTC their ass.
http://www.aclu.org/blog/technology-and-liberty-human-rights...