When those devices were invented that allowed parents to GPS-track their children, they were quickly subverted: the kids would go to a friend's house, leave the device there, and then go where they really wanted to go.
If you actually premeditate a private moment, it's fully possible to make it so.
True. You can never say for sure if your kids have privacy or not. Most kids these days don't have any notion of what privacy is, given the kind of content they are sharing on Facebook and other social networking websites.
I was with the In-Laws the other day, and overheard the following conversation between my Father-in-law and his son:
Father: "Where were you the other night?"
Son: "<name of street>"
Father: "No you weren't. Don't forget you have a car tracker to give you cheaper insurance, which I'm paying for. That means I can log on any time I like and see exactly where you were."
If you actually premeditate a private moment, it's fully possible to make it so.