Australia's soon-to-take-effect ban affects nine platforms, including Instagram and Facebook, but not HN. These bans often operate on the amount of users a platform has, so HN is unlikely to make the cut. Nobody cares about this site.
Jonathan Haidt, the most prominent psychologist pushing for restrictions on social media use for children, is also the most prominent proponent of letting kids play and roam more freely. So no, those are not the same people.
Comparing against 1990 is wrong though, as we should compare against the start of widespread social media use (2010 at least), and it's also pretty likely that other OECD countries are lagging behind with widespread adoption by a few years.
If we don't see an increase from 2015 to 2022 THAT would be counterevidence.
This is not an accurate reading of the Conclusion section. He just sums up what has been observed and does not mention any causal factors. Earlier, he explicitly says that causal factos will be covered by other posts.
While he indeed links to another article, he claims at no point in this article that coddling is a factor here.