Mobile phone apps have been around for a couple of years to track our little wizards and witches as they troll the streets for free candy.

But there's a new wrinkle this Halloween -- apps that not only track kids, but set up perimeters and alert parents when their kids have strayed too far.

New Jersey-based Snap My Life unveiled a feature last month called Geo-fence, which allows parents to create wireless boundaries on their phones and receive alerts if their phone-toting children cross them.

"It's impossible to keep your kids by your side at all times, especially as they get older, and one of the biggest concerns parents have is not knowing where their children are," said Jiren Parikh, Snap My Life's CEO.

Apps such as Life360 and MamaBear also alert parents if their kids don't show up at pre-set destinations on time. MamaBear allows parents to not only see their kids' locations, but also the paths they took to get there. Life360 links with sex offender registries to show parents places their kids should avoid.

These locator apps also work in reverse, allowing kids to send their whereabouts to parents.

The apps have limits. Wanderlust kids need only abandon their phones on the Halloween trails if they want to elude their parents' cyber-eyes. And the apps work only if children and parents have phones capable of using them.

Common Sense Media offered a favorable review of Iconosys' Trick or Tracker app, but reported in testing that it sometimes lost its signal.

The Big Brother nature of the apps draws skeptics. Reactions on the Star Tribune's Facebook page ranged from "creepy" to "ridiculously paranoid."

But the exploding market -- with Verizon and AT&T offering subscription locator services -- suggests that a wealth of parents appreciate the piece of mind.

Some older kids actually appreciate the tracking by their parents as an alternative to constant calls and texts, said Amanda Zweerink, a Life360 executive who is based part time in Minneapolis.

"This allows the parents to give, especially the teens," she said, "a little bit of free rein."