Parents worried about letting their children go trick-or-treating at Halloween can download new apps that track kids and send alerts when they venture outside designated safe areas.

With the free iPhone app Track n Treat, children send a time-limited link of their location via a phone number or email. This then allows parents to track their whereabouts via a web browser for the next four hours.

"Kids are out and about and their parents want to know where they are, so Halloween is a great use of a temporary location-sharing technology," said Bryan Trussel, CEO of Seattle-based Glympse, which creates person-to-person location sharing technologies.

Another free app, Family GPS Tracker for iPhone and Android, not only lets parents see where their children are in real-time, but also sends alerts when a child strays outside of an set area.

"With the app you can always be aware of where your children are located, and can call them immediately if they venture outside of the safe zone," said Michal Štencl, the CEO of Sygic, which is based in Slovakia.

Life360, another free app for iPhone and Android, lets family members view each others' location on a map and keep in touch via group messaging.

"A twelve-year-old might be too young to go out completely on their own, but an app can give them more freedom," said Chris Hulls, CEO of Life360, which is based in San Francisco.

The app allows users to set up zones and notifications showing, for example, when a child arrives at school, or when a spouse leaves work or gets home.

"We're trying to build a family graph," Hulls said. "You have Facebook for your friends and LinkedIn for your work contacts, but what is the equivalent for your family life?"