I believe the point is that you're lying when you say, quote, "they have to close the account".
Google could simply choose not to collect personal information on accounts of children. This would be, literally, one line of code to implement. They've chosen instead to ban children from Google services, which is in no way required by law.
Well, thanks for the "lying" comment. They don't have to pay taxes either, but that won't last long.
As for the literally one line of code, I don't believe that's correct. IANAL nor an implementor of a COPPA-compliant product, but my understanding is that even storing a copy of an email that contains personal information will be in violation of the law without parental consent and certainly without the ability for a parent to view it and delete it. Storing any received and sent email may be enough to count as collecting personal information.
Can you name any email provider that will knowingly allow children under 13 to use the service without having a parent controlling the account? When you do use the family accounts in hotmail or yahoo, you have to actually provide proof that you're an adult, and some level of proof of connection with the account (joining the accounts actually looks rather difficult, through hotmail, at least. Usually a parent account sets up child accounts). Setting up that system literally takes more than one line of code.
Google could simply choose not to collect personal information on accounts of children. This would be, literally, one line of code to implement. They've chosen instead to ban children from Google services, which is in no way required by law.