This idea has been around as long as the web, but you can't get momentum behind it.
A much better idea was a .kids domain where the content was vetted, and you could allow-list your child's device to that. Much easier than trying to migrate everyone over to specific TLDs, especially when that ship has sailed already. But that never got traction either.
Edit to add: I used to work on "family safety" software. Blocking bad content doesn't work - it's too difficult of a problem. Walled gardens do work, however. The fact that there's not a push for the equivalent of an Apple App Store for kids is probably evidence of ulterior motives on behalf of regulators.