The same argument could be said for other age verification methods. Nothing stops a kid from getting their older cousin to verify their identity for something and it will never be possible to prevent this.

The people proposing these laws presumably think imperfect enforcement is better than no enforcement at all. In the non-zero-knowledge case, it's possible to revoke falsely shared credentials.

The one where the root user can enable parental controls requires the kid to know their parent's password or save up to buy their own device.