The whole social media and under-18 argument isn't a problem with all social media.
replyIts a problem with for-profit social media. The companies use gamification to addict and create terrible trends for everyone involved.
Mastodon, peertube, lemmy, and federated media doesn't do any of these gamblification, gamification, psychological attacks, and more.
To be fair, the techniques should be banned by the FTC for deceptive practices, for everyone. But the kids angle is what's being gravitated towards.
It was bad for kids even in the BBS days.[1] The things you mentioned merely made it worse.
replyPut another way, it's as bad as your kids texting with random strangers. I know in the last decade the focus has been on all the big tech addiction mechanisms, but people were warning against them well before those came into play.
[1] It was also great for some kids in those days. That doesn't take away from the risks.