Earlier quoted context omitted.
Why isn't it enforceable? State attorney general notices his kid's social media app is giving algorithmic instead of chronological results, subpoenas social networks for number of under-18s in Minnesota, files charges, court sets up enormous fine. Which part of this process is impossible?
Kids will lie about their age. They already do. You aren't supposed to sign up until you are 13. There are lots of pre-teens on Social Media. Stopping that would mean a KYC process for every social media signup. I don't think that works either.
(or, well, not showing results to anyone)
I'm much less concerned about the issue of identifying kids (if they can't identify kids, all the better, adults get to benefit too) than that they're probably accidentally banning whole categories of useful things like rolling your own search engine.