I think this would be good for everybody, not just kids. It doesn't even have to be complicated: Just that after a certain amount of time scrolling/watching, put in a message asking if it's maybe time to stop with some information about how these algorithms try to keep you for as long as possible. Maybe a link to a government page with more information.

It doesn't have to be perfect and there will of course be easy workarounds to hid the warnings for people that want. The goal is to improve the situation though, not solve it perfectly. Like putting information about the dangers of smoking on packages of smokes; it doesn't stop people from smoking but it does make the danger very easy to learn.

Some platforms did display notices like this for a while, but I noticed that they stopped the practice after a few months.