Sounds like Australian kids will just use private / incognito browser windows (aka porn mode) even more than they do already. I fail to see what this new "policy" will achieve, apart from my above point, plus serving as an excuse for Google and pals to subject users to ever more facial recognition and to brazenly collect ever more personal data.
There's a collective action problem, though. One parent taking away their kid's phone is just isolating them from their friends, which might be a net negative. However, all the kids having their phones taken away would be a net positive.
