In my opinion the social media ban for kids in Australia is a good thing. Even imperfect legislation would be better than exposing children to the dangers. I compare it to drivers' licences, tobacco, alcohol, voting, heroin, methamphetamine. These are all things which are denied to children and it's not controversial AFAIK.
In particular the chapters in the book "The Age of Surveillance Capitalism" by Shoshana Zuboff (2019) discuss the potential damage to child and adolescent development. A lot of this would also apply to the fediverse too.
Several of the practices of commercial social media should be banned entirely, for example surveillance, not seeking consent (opt-out policies), targeted advertising, engagement algorithms. Under-16s are not the only victims.