Most cell phones already have them.Should parents use GPS tracking to monitor their children?
In the case of, say, a runaway teenager, the cell phone company can trace them down as long as their phone doesn't die.
I wouldn't say it's "practical" on a day-to-day basis, but in an emergency or potentially dangerous situation, yes; certainly.
Although it would probably be very reassuring to anxiety-raddled parents like myself to keep track of our children's every move, every second... it would not be good for the children. And in the end, it would probably just cause more friction and discontent within families.
Kids and especially teens need a long leash.
If a parent's worth a damn, kids will find their way home eventually, however far they might range.