Frankly outside of what I wrote below (which I think mere existence is still threat factor by creation of authoritarian OS for computers) you will not get 'solution' from me (unless by that you mean age rating and voluntary enforcement by computer) because you are creating the problem - You don't want to do work but want to exert control, which is contradictory and entitled position. You are not entitled to get anything, and with amount of people with kids dwindling it is beyond me why do you think 'it is for children' will even work to begin with as popular talking point. The parental controls are the best solution, assumption otherwise makes you extremist from another’s eye. Simply put the idea of computer for you is "a tool" for another it is extension of memory and mouth - you don't get control any of that, ever. There is no 'vitriol' - there is only rightful anger that you crossed of boundary of acceptable speech by another person. The most basic thing that you must get right before you start to advocate for change, is "what is my Overton window - and what is the other person's one", because thinking of workable solution works only when people windows cross to begin with - and they do not have to because sometimes you do not have the ability to have both freedom and control. And you should clearly know that for some freedom is more important than control.

The failure to do so means you get the first proposed solution - yes I agree, the first solution is by definition the status quo before the 'now' solution.

There are times that you have to accept: there is no middle ground, other than the ground you stand upon.

"Provide a solution." "can be redirected in to coming up with a workable better idea." Did you entertain the thought that there is no better 'workable' idea than status quo?

You want to control the user - kid, and not control the user i.e adult, you also want parent to not bother. That is impossible. Either parent have to do active part, other (because by definition kid already is - since the age is already available to whatever malware will be running on device) people will be harmed by surveillance or we keep status quo. Classical choice triangle.

The only "rational" (still for me this seems like possible trojan horse) way would be to actively enforce existence of "for-child OS" on company controlled OSes, and use something like Secure Boot if parent SO DESIRES (with caveat 5 ). 0. (short version) Effectively this would mean buy separate device for kids or learn how to do it. And it would fundamentally be bound to device not user, 1. by enforcing main key to be Owner's (Parent) and signing the OS developer key with the main key for purpose of OS boot (start) - so that OS 'provider' can sign kid-friendly OS version with that developer key. (you probably could ease that with vendor key - but still requires possibility of changing the key which leads to 2. then lock the UEFI by password... that still require knowledge about the tech - unless you get password in device box [then again parents have to exercise some parenting and not give device with the box], and don't start about phones - they would require UEFI and Secure Boot available for user first - not just manufacturer. 3. and you would HAVE TO (this bit is especially trojan otherwise) enforce every OS manufacturer and vendor that provide ones for kids to always provide the non-kid version (and support it!) - so that it would not create de facto surveillance OS/PC. Let me guess this is impossible for you Americans. 4. Then app developers can sign apps for kids with the OS developer key that is FOR the kid variant - otherwise will not run (in that scenario 'kid-OS' only). 5. you would have to limit it for kids devices ONLY so you would have to reverse "ID check in bar" to confirm the existence of kid instead of adult (during buying the OS/device) - otherwise again trojan horse (because of commonality of solutions).

If you find this version 'workable' please have it - but for me it seems contradictory to desire of not bothering parents. *From my perspective this is effectively parental controls on steroids*. This is exceptionally similar to attestation except it has opt out for people who actively kept the password, no IDs, and no 'sending age over wire'. This will help exactly zero to stop spread of some files if parents give a kid in class for-adult phone/pc unless you enforce signing every file by kid-OS and not opening unsigned files - congratulations your kid would be using OS approved by north Korea! - do you start to see the issue with 'workable' ideas? They inevitably flow to surveillance and autocratic tech.

This is anyway probably faulty in something I did not thought about.