I don't think that it matters. The big porn sites have served RTA tags for many years. Android, Windows, macOS, and iOS can all be configured to block adult content tagged with this system. That still hasn't stopped a bunch of states from passing age verification laws ostensibly targeted at protecting children from these sites.
In order to accomplish that working, you'd have to legally mandate parents put the blockers on their kids devices.
Similar things exist that block based upon lists and content keywords and such.
Most parents do not want to block stuff from their kids or they would be.
If thousands of them demanded that devices came with blockers then the market would provide such devices.
Many moons ago you could argue parents did not know what the youngins would find on the internet. Today's parents definitely know, and most do nothing to restrict access.
It doesn't have to be mandated - parents could choose.
Even if it's mandated that kids can only use phones with a special "kid mode" turned on, even if you had to present ID to turn it on or off or buy a phone with it turned off, that would still be way less bad than what's being rammed through parliaments right now.
