05kids-190.jpgED GRAY’S two teenage daughters wanted cellphones, but the answer was a firm parental no — until Mr. Gray learned about a service that changed his mind.

C. J. Gunther for The New York Times

THERE Ed Gray bought phones with G.P.S. to track the locations of his daughters, Tiffany, left, and Jasmine.

Sprint Nextel and Verizon Wireless offer G.P.S. tracking to let parents know the location of their child (as long as the child has a cellphone and it is turned on). Then, if the child doesn’t show up at school or other location at a certain time, parents can arrange to receive an e-mail or text message alert.

Mr. Gray, who lives in Granby, Mass., decided that the comfort of regularly knowing the whereabouts of his daughters, Jasmine, 16, and Tiffany, 15, would offset the pain of paying for cellphone service for them, especially if the additional costs were modest. So about five months ago, the Grays signed up for a plan with Sprint that includes Family Locator, a service that for $9.99 a month lets a parent track the cellphones of up to four children.

So far, the deal is working well. “The girls have cellphones, and we foot the bill in exchange for peace of mind,” said Mr. Gray, who is a technology support specialist for the alumni association of Mount Holyoke College and the author of a blog, Ed’s Tech Tips.

When Mr. Gray uses the service, he turns to his computer and clicks on the Sprint Web site to locate either child. “Within about a minute, an icon appears on a map showing where the phone is,” he said. “It’s easy to use. And it’s good to be able to keep in touch when you need to.”

Sprint offers about 90 phones for children that work with Family Locator. Parents can monitor children’s phones not only from their desks, but also from cellphones that can search the Web. By calling up Sprint’s Web site, a parent can see the child’s phone location on a map or listed by street address.

A location’s accuracy is typically within 50 to 100 yards, said Rich Pesce, communications manager for Sprint, in Reston, Va. “If the phone can’t communicate with the G.P.S. satellites, it defaults to cell-tower locations and estimates the distance from them,” he explained. Then accuracy drops to about a mile.

Sometimes the system cannot locate the child’s phone, Mr. Pesce said, usually because the phone is off or out of range of network coverage.

The service isn’t meant to be covert. Parents can choose either to have an alert pop up on the phone every time they check its location or have occasional notices sent to children reminding them that their location is being monitored.

The Grays chose a Sprint family plan with an $89.99 monthly charge that includes 1,400 minutes. They added unlimited text messaging ($20) with the location service (about $10). The bill totals about $140 a month, Mr. Gray said, including $20 for the daughters’ two phone lines. His daughters, he added, put up with the parental monitoring because they wanted the phones so much. Verizon Wireless’s service, called Chaperone, allows parents to set up a geographical area where the child can roam — a downtown shopping district, say. But if the child strays from the zone, the system alerts the parent.

Some children will no doubt foil the system, for instance, by simply leaving their phones behind. But many parents may still find the tracking services attractive, said Charles S. Golvin, an analyst at Forrester Research. The services, he said, “are complementary to one of the main motivations adults have in giving children cellphones — to get in touch with them in an emergency.” Adding the ability to know where they are ties in to this. “It’s a comfort to have a bit more information,” he said.