How does this solve the problem at all? You're just making more problems. Now you have to deal with a black market of "unlocked" phones. You're having to deal with kids sharing unlocked phone. Would police have to wal around trying to buy unlocked phones to catch people selling them to minors? What about selling phones on the internet, would they check ID now?

SOME parents give their children access to their ID. That is NOT the same as ALL parents, and therefore is not a reason not to give those parents a helping hand.

Even just informing children that they're entering an adult space has some value, and if they then have to go ask their parents to borrow their wallet, that's good enough for me.

It would not be solved without a culture shift. But with a culture shift, giving a kid an unlocked device would be as rare as giving them drugs.

I'm sure it will occasionally happen. But kids are terrible at keeping secrets, so they will only have the unlocked device for temporary periods, and I believe infrequent use of the modern internet is much, much less damaging than the constant use we see problems from today. A rough analogy, comparing social media to alcohol: it's as if today kids are suffering from chronic alcoholism, and in the future, kids occasionally get ahold of a six pack.