The world you describe is not plausible from a technical perspective. Any kid who wants to will be able to download a tool that will enable them to surf the net like an adult. It will be as common as our access to cracked C64 games during the 1980s. The only thing to limit this in any reasonable sense is to crack down hard on all operating systems and network software.

At the very least, you will need to make sure that no child can install Linux. Otherwise, why wouldn't they? Most kids aren't stupid and want to know what their braindead parents are doing on the internet.

I really believe it's dangerously naive to believe this is about the children. It's quite obvious why suddenly ominous entities are shilling for age verification, digital IDs, digital wallets, and so on (more is to come). Countries in the EU used to get valuable SIGINT from the US that prevented many serious crimes. They still get it but now they've realized that the US might not always remain aligned with them and panic because they have almost no access to modern operating systems except for buying 0-day exploits on shady black markets. They desperately need to get their foot in the door to get the right surveillance infrastructure going. At the same time, politicians are rightly worried about the influence of bots on elections.

These are the principal reason why governments are suddenly pushing for this. If this was about the children, they'd have done it 30 years earlier. Until very recently, this discussion didn't even exist. It's manufactured.