A host of new products that help parents keep tabs on their children are hitting the market, including one-touch phones and even electronic tags that can be sewn into clothing.

Some technology-based trackers have been available before, but many of the previous products have required parents to be sitting at a computer. The latest services offer more mobility. Sprint Nextel Corp. recently launched its "Family Locator" service, which enables parents, using their own cellphone, to pinpoint the location of their child's mobile phone. It costs $85 for the handset (with a one-year contract) and $9.99 a month for unlimited location requests. Another company, Wherify Wireless Inc., plans to begin selling a mobile phone in August, called Wherifone, that will have a one-touch "find me" button to reach a parent instantly in an emergency (it sends an instant message to the parent's phone). The phone will be priced at $99.95 with a one-year contract, and service will cost $19.99 a month for 100 requests.

Knowing where your children are is an age-old parental challenge. The proliferating use of cellphones among teens and preteens in recent years has been a huge advance, enabling parents to stay in contact with their children, wherever they are. But cellphones merely allow parents to speak to their children, not to pinpoint precisely where they are at a given moment. Moreover, toddlers and other younger children, who may be prone to wander away in crowded places, are too young to have a mobile phone.

In part to address that gap, other companies are rolling out tracking products that work over short distances and don't require cellphones. SmartWear Technologies LLC in San Diego, which uses the "radio frequency identification" technology that Wal-Mart Stores Inc. relies on to manage its inventory and that cities deploy to read water meters wirelessly, plans in the next few months to begin selling RFID tags that can be sewn into children's clothing or embedded into a wristband. Using a "reader," parents can keep track of their children's movements as much as 600 feet away; the whole package costs $260.

The new services are being introduced as wireless carriers like Sprint and Verizon Wireless struggle to meet new federal regulations designed to make it easier for police and other emergency agencies to pinpoint the location of cellphones. Sprint and Verizon Wireless didn't meet the Dec. 31, 2005, deadline for 95 percent of their customers to have the right type of handsets. Industry analysts say the two companies are hoping that by offering added features more customers will upgrade to phones enabled with Global Positioning Service, or GPS, a requirement for the new features.

Developers of these offerings say they will give parents some extra peace of mind at a time when other new technologies, from social-networking sites like MySpace.com to instant messaging, have made parents feel more out of touch with their children. Civil-rights advocates say they infringe on children's privacy and have other Orwellian implications.

"There is a difference between talking to your kids and sniffing your kids," says Lee Tien, an attorney with the Electronic Frontier Foundation, a nonprofit digital-rights organization in San Francisco.

Critics also worry that hackers may be able to access the location information and are concerned about the government's possible use of GPS and other technologies in ways that jeopardize civil rights.

Technology companies say they have been sensitive to these security and privacy concerns. For example, with Sprint Family Locator service, children are notified by a text message each time their location is provided to their parents by Sprint. "This will ensure open communication" between parents and kids, says a Sprint spokeswoman.

SmartWear says the company has set up a centralized system with multiple security steps that ensure only authorized people can access the information stored in their chips. "You might have more personal information listed in your local Yellow Page than on a chip," says Evan Jennings, a company spokesman.

GPS has long been used in the business world to monitor everything from delivery trucks to cargo ships. In recent years, it is increasingly turning up in newfangled tracking devices for parents, including watches and backpacks.

They haven't always been a success. In 2002, Wherify rolled out a GPS watch for children that didn't sell well, and the company discontinued it last year. The $400 price tag was too high, a company spokesman says.

Jacqui Jo Fahrnow, a single mother in Shawnee, Kan., recently subscribed to Sprint's service. Now, she says, she doesn't worry when her teenage sons are late from their basketball games. She can tell their exact locations using the phone -- even if they are in the middle of a game and can't answer it. "It's not about control. It's about their safety," Ms. Fahrnow says.

The service enables a parent to locate as many as four cellphones, and parents also set alerts to notify them when a child arrives at a specified location, such as a school or home, at a specific time. It costs $10 to $25 a month extra to use the wireless Internet.

The same technology that drives the SmartWear tags is used in Denmark's Legoland, one of Europe's biggest amusement parks, where parents can rent special tracking wristbands for their children to wear in the park. If a child wanders off, the parents can send a text message from their cellphones and receive a reply telling them where to find their child.

Disney Mobile of Walt Disney Co., which leases Sprint's network to provide wireless service under the Disney brand, will launch a service in June, also called "Family Locator." It's similar to Sprint's but won't have the preset safety alert feature. The price isn't yet available.