If you don't want to allow < 13, you just need to make sure you ask and don't accept people who reply with < 13. It then becomes the kid's legal guardian responsibility to make sure the child doesn't use the service.

If you do want to accept it, you need to use IRL methods (phone call, credit card, etc).

Am I reading this properly or did you suggest that Google should be above the law?

They download/copy content from millions of sites without explicit permission.

Of course that example is more ambiguous as the definition of fair use is vague (and ever-changing), but is not all that different.

If every business followed every law in the books the economy would crawl to a halt.