Would it not be possible to have a rating system like for films? (X, R, PG, etc)
Seems like it would be really hard. A TV channel or studio puts out dozens of shows at a time. Something like Youtube gets its content from its users which upload gazillions of videos a day. Content would have to be rated by AI. They already make you sign in if it's flagged as adult content. Google has option to restrict adult images in search, again very likely done by AI.
I don't see this as a massive problem. Anything on the web illegal, like people planning terrorism, would probably be watched by authorities anyways, again with help of AI.