While cellphones are increasingly popular among kids, some scientists worry the devices are a health risk to them. The World Health Organization is completing a massive study to see if there's a link between cellphone use and brain cancer and other ailments.

Cellphones emit electromagnetic radiation and their design requires them to be held close to the user's head. Scientists are concerned that childrens' skulls are thinner and their brains are still developing. Therefore, the risk of electromagnetic energy damaging their brains could be greater than the risk for adults.

A Canadian research team contributing to the project has access to the phone records of cancer patients -- including some children.

"And if we're looking at chronic diseases like cancer, because they are exposed at an earlier age, they have a greater opportunity for that effect to manifest itself," said Daniel Krewski, one of the Canadian researchers, who added there is no evidence so far that kids are at risk.

One reason for the growing concern is that the wireless industry is increasingly targeting children. Already on the market are Hello Kitty phones, offered jointly by Nokia and the character's creator, Sanrio. Mattel sells a Barbie-branded phone as part of its My Scene line targeting 8- to 14-year-old girls. Verizon Wireless has added Sesame Street and Nickelodeon clips to its V Cast wireless broadband service.

Most prominently, the Walt Disney Co. is teaming up with Sprint to offer wireless phone service with Disney-branded content. The new program, called Disney Mobile, will be offered next year and will target families and the growing number of kids with cellphones.

A Disney spokeswoman said the phones will offer Disney-branded "ring tones, graphics and information," but she gave few other details about the service.

Children have become a favorite new market for mobile services now that most adults - over 80 percent, by some counts - already own cellphones.

According to NOP World Technology, a consumer research firm based in Manhattan, 40 percent of kids aged 12 to 14 owned cell phones at the end of last year, up from just 13 percent in 2002.

There are ways to reduce the risk of brain damage, said a WHO spokesman.

"With respect to children, WHO recommends that children should use hands-free headsets," said Mike Repacholi.

While the risk may be slight, the WHO notes that the vast number of cellphone users means that even a slight risk can have a major impact on public health.

Cancer isn't the only focus of the WHO study, which will also look at conditions like memory loss and other decline in mental functioning. The study is also examining the questions of whether people can safely use cellphones while driving and how much they interfere with medical devices.