> but if it can be unlocked to run arbitrary software then he can in theory unlock it.
I'm effectively the admin several machines with many users on them. I have root access. I'm not at all concerned that they'll gain root access. Just make yourself admin on your child's phone, I don't see the issue. Apple and Google can even make gaining root access require some technical (but documented) methods. Look at the requirements to gain root on an android phone currently. You should be comfortable going into a terminal and using ADB. I'm not worried about the average user doing this nor even the average smart child. Hell, follow Apple's lead and require a 1hr lockout if you're really concerned about someone getting root on your device. How often will that happen if it requires being connected to a computer for an hour?
