Our next generation will probably have their own smart phones before they have their own computers. That means they have their own personal unmonitored internet connection, and for paranoid parents that's a huge red flag. Whereas normal desktops can be placed in common areas at home to discourage inappropriate use (whether deliberate or accidental), mobile phones don't have that option. When there's an internet connection in everyone's pocket, what do you do? You can try locking it down so that the user (the child) is not an administrator (the parent) who decides what is and is not acceptable on the phone. That kind of system has to be perfect to be successful, though, and nothing is ever perfect.
Mokalus of Borg
PS - Maybe it would be good enough for most circumstances, though.
PPS - And it all depends how much you trust your kids.