> protect their children
Going "entrance forbidden to the libraries and bookstores: they are full of bad texts (and there are people scribbling dumb harmful things on the billboards there)" is not "protecting children".
(With reference to YouTube, chiefly, but not necessarily excluding other repositories. And not to mention the actual intention to block access to encyclopedias.)
It's not entrance forbidden to libraries and bookstores though, it's closer to entrance forbidden to bars and casinos. Modern social media is quite low value and quite predatory.
I think that depends a lot on the age of the child in question. I absolutely would simply forbid an 8 year old from entering a library or book store with neo nazi writings or aum shinrikyo literature or Ted Kaczynki’s manifesto easily accessible. Trying to provide appropriate context for everything at that age is simply not feasible.