I think this is a great idea, if a parent finds it necessary to know where their kids are, then they should have every tool available for it. Don't talk about trust, because parents know when kids deserve trust, and this tool wouldn't be necessary. But for those kids who obviously don't deserve this trust, they SHOULD be tracked and accounted for. It's like that commercial...It's 8pm, do you know where your kids are?
As for kids just turning their phones off, or wrapping it in foil...I doubt they would want to do that because it would block incoming calls as well.