Given all the backdoors and remote access stuff that are in place already, surely it should be a piece of cake to give parents some sort of remote access to their children's phones ?
And what about enforcement? So you see bad stuff on your kid's phone repeatedly...in the end all you can do is take it away. Then they go to the computer. Then you take that away. Then they stay after school to use the computers there. Really I don't expect the symptom mitigation solutions to be very effective.