User blog comment:ForestFairy/How to Take the Fun Out of Trolling/@comment-14727181-20150606091237/@comment-1038387-20150606105618

Just to get this common misconception out of the way: underage (i.e. under-13) users do not break "the law" (or, specifically, COPPA). They break the Terms of Use.

COPPA applies to US-based companies, such as Wikia, Inc. The digest version: they are only allowed to store personal data of under-13 year olds with a shedload of safeguards and parent permissions etc. to safeguard the kids' privacy and online security that Wikia (and many other sites) decided to not allow them on altogether. Wikia would be the one breaking the law, and to prevent that, they put that point in the Terms of Use.

As noted above, a local wiki's admins do not have to block under-13s they encounter. They can report them to Wikia Staff via Special:Contact/general. However, they have no legal obligation to do so, and will not be held accountable if they don't. It's a Terms of Use issue, so it's between the user and Staff.