"Parenting and parental control applications."

Correct. For the life of me I cannot see how this can ever work in practice.

For such a scheme to work all users would have to be physically and electronically locked out from accessing any feature of a computer that would alter its function.

This has to be sheer madness. Every general computing device from small embedded controllers, to Raspberry Pis to the most powerful desktop computers would have more in common with electricity meters and their embossed lead anti-tampering seals than present-day computers. Can you imagine the utter chaos of the state conducting regular anti-tampering audits of every state-registered PC? And what about the millions of legacy PCs that could not be adapted?

Moreover, using such a computer would be more akin to using an automatic teller machine with its strictly controlled and limited functions, the notion of "general computing" as we now know it would cease to exist.

The only practical solution is to make parents responsible—that is to ensure their kids do not have unfettered/unmanaged access to computers. Responsibility could be extended to all adults, anyone deliberately providing unsupervised/unfettered computer access to minors could be charged with child abuse.

If parents aren't prepared to extend their parental responsibilities to also include computing devices, phones, social media and such then the state could impose penalties. Of course, for that to work society would have to agree as it now does over outlawing the physical punishing of children (not that long ago that wasn't the case).

No doubt arriving at a society-wide consensus would take time but it's doable. Societal views do change, for example, when I was a kid we got the cane for misbehaving, caning kids is now outlawed often with heavy penalties.

Finally, I also find your point about the age verification debate popping up simultaneously in the US, UK, and EU as very troubling. I'm not a conspiracy theorist but evidence suggests there are many lobbyists acting behind the scenes of whom we are unaware (same goes with the encryption debate).

It's this sort of hidden subterfuge that's undermining and pulling our democracies apart. Little wonder that these days many citizens have little faith in institutions and those whose governance they're under.