This is actually a key consideration for the proposed implementation. The biggest issue for parents when restricting their children's online activity is that they simply don't understand the tool available for it.
By having a "child mode" iPhone, parents don't have to know any of that. They simply buy the iPhone Kids for their children and then get a plain iPhone for themselves.
If these restrictions were to actually be enforced by law as well, then it would make it very easy for teachers and other guardians to check if a device is appropriate for the child using it.
So if the teen phone turned into a restricted "call mom" device with no cameras and with neon yellow obvious fuck you coloring and a restricted set of apps, and police took away a full phone much like they take away cigs and beer it might be enough to break the critical mass to create this issue. They can have dedicated cameras for video club, use the family computer, have an xbox or switch and have whatever tech experience that millenials had, the last generation to not have exponential increases in anxiety , depression and sexlessness.
It's the covert camera + internet that it's the key issue.