Verizon Wireless, the No. 2 U.S. cellphone service provider, plans Monday to launch a wireless service that lets parents check their children's whereabouts and alerts them when they venture out of bounds.

Parents can use the service to set up geographic limits and recieve text alerts if their children, who also carry phones, go too far from home. The service also lets parents check where their offspring are via a map on their cellphone or computer.

The Chaperone-branded service from Verizon Wireless, a venture of Verizon Communications (VZ) and Vodafone Group Plc , follows in the footsteps of a similar service that Sprint Nextel Corp. (S) introduced in April. Entertainment conglomerate Walt Disney Co. (DIS) is also set to offer a similar service when it starts selling cellphones this summer.

Such services are aimed at bringing in revenue from a location technology that U.S. wireless service providers are required by law to put into cellphones so that safety workers can pinpoint the location of 911 emergency service callers.

Mobile packages designed for families have become key to growth at U.S. operators, which currently sign up as many as 60 percent of their new subscribers via family discount plans, according to technology research firm Yankee Group.

Verizon Wireless did not say how many of its customers have children in the 5-year-old to 9-year-old target market but an executive concurred with the Yankee estimates on family plans and said the market for this service could be big.

"You're looking at a good percentage of customers that have families with children," said Jamal Jones, Verizon Wireless manager of consumer products, in a conference call with reporters Friday.

The Verizon service costs $9.99 a month for just the location-viewing feature and rises to $19.99 a month if the parent also opts for a boundary-setting feature. Sprint charges about $9.99 for its service.

Verizon is initially launching the service just for parents with children using the Migo phone from LG Electronics Inc , a four-button phone designed especially for children. Verizon started selling the Migo in November.

Executives said Verizon Wireless may develop a version of the service for older children, using more sophisticated phones, but they did not give details.

Parents can access the service using about 10 different phone models sold by Verizon Wireless including several phones from LG and some phones from Motorola Inc and Samsung Electronics Co Ltd.