Part of the problem with COPPA and other laws that deal with how websites operate (such as PCI compliance) is that's difficult to distill what is technically required from the legalese. COPPA is often summarized as "you can't store personal information about children". Unfortunately, as I've seen from my clients, that can be interpreted as extremely as "children can't have online accounts" or as lightly as "tick this box to show that a parent approves this child's account".