The law states that a site may collect information with the consent of the child's parents. That is fairly innocuous. The problem is that Google scuttles the account and thus the Chromebook.
At Google's scale, I think it definitely makes sense to put the extra engineering effort in to comply with the law while the kid is too young.
On the other hand, I'd probably sign up as a 5 year old if it meant Google would collect less information from me and show fewer ads. Paid account?