But at the same time, why bother. They will quickly figure out that they can access all of nostr from any other client. Every phone has a web browser.
Discussion
Yes, basically an app for parents or some NIP that let an npub to control another npubs following list for example may work.
About finding out stuff in other clients, it's mostly something related to the parents and how they manage to keep them safe from the bigger internet space!
For us, it's important to give this safety control to parents, not government and KYC.