Children do not want child locked devices and they will find alternatives

The issue is not just age verification but also device pinning.

I think the framework here is to have community driven age verifiers( i recall there is an EU effort for digital wallets which besides it's bad parts has some of these good parts) which can verify ages for people and link them to( local biometrically encrypted) devices for pinning. This would be privacy preserving. The only downside is a mandate for all devices have a built-in hardware biometric encryption like a finger/face print so phones can't be just(used) with these apps installed.

The verification part is a job that could be done by all the teachers and coaches and ofc parents. Any one verifying identities would be cryptographically nominated/revoked by a number of more senior members of the community. A prent always get the right to say ok for their kid ofc but so could teachers or legal guardians..

We(legally) need a mandate for smart devices to have local device only biometric verification. The law should be to have these apps follow device app store protocols.

As with smoking, alcohol, sex, drugs etc

Children who are smart enough to get access to a given vice without getting caught are more likely to be mature enough to be able to cope with that vice.

True, it's never going to be 100%, but at least it's a tractable problem for parents. Enough to change what the culture considers "normal," anyway.

Imperfect solutions are still called "solutions".

Well then don't give them money to do so, its not like phones grow on trees. If you make selling phone/internet device to a minor under certain threshold an illegal act severely punished by law in same way alcohol and cigarettes are, many cases of access are solved. Also, paid internet subscription doesn't grow on the trees even though there are free wifi networks.

All imperfect solutions, but they slice original huge problem into much smaller chunks which are easier to tackle with next approach.