SMART phones, MP3 players, laptops and other devices are the air kids breathe - perhaps too deeply. A new US study shows children ages eight to 18 devote an average of seven hours and 38 minutes a day consuming some form of media for fun. Leanne Italie plugs in. Like many working parents, Beverly Flaxington armed her daughter with a cell phone in fifth grade - about 11 years old - when the time came for her to venture out alone.

At first, it was a great way to stay in touch.

That was then.

Now 13, Samantha's grades have slipped drastically, and she is obsessed with texting, Facebook and her laptop, sometimes falling asleep in her clothes clutching her phone. When her texting exceeded 2,000 messages a day, her parents shut off the function from 9pm to 6am on school nights, and Sam "just went nuts."

"She slammed doors. She accused us of being overly conservative when all of her friends are able to do things at night," says the mom in Walpole, in the US state of Massachusetts. "She didn't speak to me for three days. She broke things. You're left with the choice of, 'Do I make her a leper because she's not a part of this or do I just spend all of my time fighting'?"

Smart phones, MP3 players, laptops and other devices are the air kids breathe - perhaps too deeply, judging from a study that shows children ages eight to 18 devote an average of seven hours and 38 minutes a day consuming some form of media for fun. That's an hour and 17 minutes more than they did five years ago, said the study's sponsor, the Henry J. Kaiser Family Foundation. And today's children are champion multi-taskers, packing content on top of content for an even heavier onslaught.

"This is a game changer," coauthor Donald Roberts said during a panel discussion when the survey of 2,002 young people was recently released. "We're really close to kids being online 24/7."

Children, the survey showed, now spend more time listening to music, playing games and watching TV on their cell phones than talking on them. Perhaps more surprising: Only about three in 10 said their parents have rules about how much time they can spend watching TV or playing video games.

Not all parents consider all that time spent on technology a bad thing. Craig Kaminer's 19-year-old and 16-year-old sons have laptops, high-speed Internet connections, Xbox, HDTV, iPhones, video chat, iPods, GPSes, DirectTV with DVR, Kindles and digital cameras.

"They're connected to the Internet, each other and us from the second they wake up until they go to sleep," says Kaminer, of St Louis, Missouri. "In general, they're very grounded and handle the balance well."

Others, though, find balance elusive. Things changed for Betsy Tant in Knoxville, Tennessee, when her 11-year-old daughter received an iTouch for Christmas.

"She's obsessed with it all of a sudden," says Tant, 40. "That really caught me off guard. She's had a computer for a while, but now she wants to check her e-mail all the time. We've had to set limits."

Tant considers herself an exception in the limit-setting department, refusing to provide her daughter text service, for instance. Many parents she knows don't bother.

"It gets them out of their hair, I think," she says.

With so much temptation - Internet-equipped mobile devices, better home connectivity, video gaming online and off, social media and TV-like content on any device - many parents say schoolwork is suffering.

The researchers warned that further study is required to link media use with any impact on the health of young people or their grades. But 47 percent of heavy media users among those surveyed said they earn mostly Cs or lower, compared with 23 percent of light users. The study classified heavy users as consuming more than 16 hours a day and light users as less than three hours.

Flaxington, 49, learned in November that her teen went weeks without turning in homework in math and other subjects, so they arranged for her to complete assignments at the end of the day at school, where cell phones are banned and computers were not available.

"It was impossible to get her to focus at home," Flaxington says.

Dr Russell Hyken, a therapist who specializes in tweens and teens, is seeing a growing number of young patients with obsessive interest in gaming and computers, including a high school junior who took to urinating in a bottle while playing online and a college kid who shaved his head to save time on hair washing in the shower so he could return to the computer more quickly.

Both, he says, were sent to residential treatment programs for those and related problems.

"It's almost an obsessive-compulsive desire to be the best. One client had to be in the top five scores on a Website at which half a million people were playing," Hyken says. "They're using it as a way to escape reality."

Marci Gerwe in Nashville, Tennessee, considers herself among the lucky: her boys, aged 13 and 15, abide by family rules. No laptops after 10pm. No video games during the week unless they are exercising at the same time. And absolutely no texting during meals.

Still, she says she has watched their habits change dramatically in the last two years.

"With texting and Facebook, I'm seeing there's a whole loss of ability to interact or talk on a more personal level, especially for my older one," she says. "There's a lot of confusion over what people mean."

And many parents report less than stellar success with imposing restrictions on mobile devices and computers. Young people are geniuses in finding ways around them.

Beth Shumate, who lives near Dallas, Texas, says her 13-year-old and 15-year-old boys are so obsessed with the massive online quest game RuneScape that she locks the laptop, keyboard and mouse in her car at night.

Before she took that step, "I caught my 13-year-old playing it at 5:30 in the morning."

Hyken says there's no way around the need for parents to take charge. He suggests setting up a central location far from bedrooms at night to plug in all devices, and holding firm on no TV or computer use after certain hours, with absolutely none during meals. Encourage extracurricular activities away from home, where use of mobile devices would be impossible, like sports.

"It's never too late to start but much harder when they're 15 or 16," he says. "If a kid is making good grades and is in some extracurricular activity or working part-time, and they're nice to their parents, you've won the game."