Locked down devices will never preserve privacy since the government can just mandate spyware that you won't be able to remove.

There is no form of digital ID that isn't evil, but anything requiring attestation is super evil.

Client-side filtering solves the problem, because children's clients are owned by their parents. We should mandate that websites and apps send metadata about the content being served (eg extending the Rating: RTA header from 20 years ago) and mandate that OSs/browsers allow filtering to be easily configured at setup. This is a more private but also much more granular/useful solution, it's only difficult today because of a lack of coordination