Some Legoland theme parks are now fitting kids with tracking RFID bracelets when they walk in the gates. Parents like this because they don't have to fear that their kids will wander off and get lost within the park. Legoland likes it because they get more data on which attractions are most popular, and so forth.
But here's something I hadn't thought of. When parents know they can find their kids at any time, they're more likely to let them wander out of their sight. The trend over the past few decades has been more and more parental oversight all the time - supervised soccer teams and organized play dates instead of wandering down the block to see what the neighborhood kids are up to. As much as I worry about the possible lack of privacy for kids (especially teenagers) if GPS or RFID tracking grows from amusement parks to everyday life, maybe there's a silver lining here. If Mom knows she can locate Johnny whenever she needs to, maybe she won't feel the need to know his location every moment of every day.