You can just be explicit. We already do this with controlled substances, maintain a defined regulatory schedule, and give a designated regulatory body a legally prescribed process for adding to it, removing them, or changing their classification.
If they have a set of characteristics that line up with social negatives, they should be disallowed or not permitted for persons under N years old (like for gambling or smoking). This doesnt solve the problem for adults of course, but its a good compromise.
I would very readily be in favor of outright banning infinite scrolling video feeds, even if its just for under 18s