Comment by Terr_

Also, (b)locking at the device level has a crucial benefit: It brings enforcement into a physical realm where parents can detect and manage exceptions.

If Little Timmy has a phone you don't recognize in his hand, then you know that's a problem.

It also insulates every website from needing to support Orthodox Latverian messianism where male children below the age of 17 lunar years cannot see unclad ankles.