Tracking apps for phones are nothing new, but most of them require a computer to see where the other person is. A new iPhone app called Whereoscope make tracking much easier, and by working in the background, could allow for surreptitious snooping.
Whereoscope lets you set up what are called Geofences for your kid's frequently visited spots such as school or a friend's house, and when they move outside those zones you will get a message to let you know. The clever part, is that by only switching on the GPS when the kid is moving, Whereoscope doesn't run the phone's battery down too fast.
The service also treats parents and children equally. They see the same information Whereoscope says that's essential to making the children enjoy the service rather than resent it.
The main catch right now is that both ends require an iPhone running iOS4.
Whereoscope is available now in the iPhone App Store.