I imagine it’ll be quite socially stratified - upper-middle class parents will be giving their kids dumbphones and keeping them off social media, possibly sending them to ‘tech-free’ schools, while poorer parents won’t.

Unfortunately this seems quite plausible from today’s POV. As the old saying goes if you don’t want to be the product, you’ll have to pay for it. And I see only a silver of people being rich enough to afford and educated enough to care for paying privacy- or sanity-preserving tools and services.