COPPA is a US-only rule barring 13 or younger people from communicating in forum space, etc that would allow the minor to share personal information. so COPPA users on CS have limited access to many parts of CS, including the forums. this part of the rule specifically seems to apply to cs:
"Making personal information collected by an operator from a child publicly available in identifiable form by any means, including but not limited to a public posting through the Internet, or through a personal home page or screen posted on a Web site or online service; a pen pal service; an electronic mail service; a message board; or a chat room."
(
from the text of rule, more info on COPPA here form the FTC)
it's a pretty ancient rule in the scheme of the internet, honestly don't see it referred to by name often anymore. most websites just bar 13 year olds all together.