> In the context of social media, if they want to actively participate they have to given that it's the entire point.

If the kid signs up for e.g. TikTok and the adult neither uses nor has any intention of using that platform, what causes them to even notice that it's happening?

Social media also seems like a pretty obvious case for this not working at all because if you ban kids from the ones based in your country, they'd collectively sign up for one based in a different country that doesn't enforce the ban, and the network effect for that age group shifts there because of the ban.

> It's true that even with a government ID scheme people could borrow someone's ID to get passive access with their consent.

That seems like the main problem though? Even if it actually prevented them from posting, you're conceding that it neither prevents them from doom scrolling nor accessing pornography, which are both passive consumption.