There is a serious problem with this stuff on the Internet, but there are existing private solutions you can install either on devices or routers to address this question. Have you tried these solutions and how well do they work?

The big problem is: how far do you extend the block?

I mean, if you let me write the blocklist I'd put the Daily Mail on it (persistent racism, homophobia/transphobia leading to suicide, and the sexually exploitative "sidebar of shame" commenting on women's bodies). I can't imagine getting universal support for that opinion. Other people might go in the other direction and demand that all material that even mentions homosexuality be banned.

If I had kids, I'd definitely want to block them from reddit and 4chan until at least mid-teens. I note that, on my EE mobile phone, there is some URL filtering that blocks NSFW subreddits (and also a few random blogs for no discernable reason). But it only works on http, not https, making it kind of a figleaf.

Second real, difficult to address problem: use of social media for bullying. This includes nonconsensual circulation of nudes (tricky one: should be severely punished, but not by putting kids on the sex offender registry).

I went to school in an era when, if you wanted to get adult material off the internet, you had to wait for the guy who had the modem to download it to floppy disks and circulate it in the playground. Now consider trying to block "samizdat" porn on SD cards.

(Also, wasn't there a thing on HN a while back about attempting and failing to automatically detect people building penises in LEGO's MMO?)