If adults can lose minutes at a time and forget why they pulled out their phone because of social media, then image how much of stronger effect it has on kids. It doesn't take a psychologist to come to the conclusion it's probably not healthy for kids.
Within reason, adults can do whatever they want. We also have laws saying they have to be 21 to drink and own hand guns. They have to be 16 to 18 to get a driver's license. Kids can't even get into an R rated movie...legally. Yet many parents have no probably letting their kids doom scroll on social media and YouTube. And have access to the open internet. It may not be as bad as smoking and drinking, but it is clearly mostly a waste of time to stare at an endless feed of short videos, photos, memes, and short paragraphs curated by an algorithm designed keep you watching as many ads as possible. That would be true even if it wasn't radicalizing people.
Social media is just as obviously a net negative as smoking cigarettes to anyone who partakes. Just like smoking, that doesn't mean there are not positives too. But on balance we all know how we use it the most its is at best is a waste of time with a potential of lots of negative consequences. It is right to have laws designed to keep kids off these platforms. I mean, heavy forbid they have to have a text chain, and instant messaging group, actually call someone, or see their friends in person.