I mean knowing where they are doesn't tell you if they are doing something they should not be doing, which after watching the trouble these kids in this neighborhood get into between 3pm and 6pm before their parents get home - trust me you better find out what your kids are up to, not just where.
But our belief is that there's also plenty of times when you really do just want to know where they are. If you're a busy person (say you're a single parent who's at work when their kids arrive home), being able to quickly check that your kids got home ok is huge piece of mind, for a very small time investment. Also consider the equation when you've got a few kids running around -- being able to open our app and see where they all are in a second or two is going to be easier than calling them all up. There will also be times when you're in a meeting and discreetly checking this app is going to work much better than running outside to make a few calls and track down all your children.
I think they are going to learn to come home, leave their phone there (or at a friend's house) and then go do whatever they want, secure in knowing they are definitely fooling mom/dad.
So you are right back to where you were before they had a phone at all.