User blog comment:Aj732/PROTEST/@comment-26254837-20150806195022/@comment-1038387-20150806211243

"parents' permission", or as the law calls it, verifiable parental consent, is a judicial minefield. It's not "oh hi, I have my parent's permission, I can go on". The party subject to the law (Wikia) has to seek out the parents and acquire their permission either before or, within a reasonable timeframe, just after collecting the information (i.e. a user registering). Since that is impractical on a large scale, many large companies choose, like Wikia, to not allow under 13s at all. They are within the law to make that decision, and it helps them comply with the law.

See this very useful document from the FTC on this: Complying with COPPA: Frequently Asked Questions. It's written from the perspective of those affected - companies, not users.