Teenage girls are almost glued to social networking sites by the time they reach age 15, a Perth study has found.
In some of the first research in the world to track total screen use in children from the time they wake until they go to sleep, University of WA researchers found 80 per cent of 15-year-olds and almost half of eight-year-olds use screens for more than the recommend two hours a day limit.
Their study of more than 2600 WA students aged eight to 16 argues that current advice on how much children should use television, computers, smartphones and tablets is out of date and "virtually impossible" to enforce.
Excessive screen use has been linked to poor physical and mental health, including an increased risk of depression and anxiety in teenage girls.
The American Academy of Pediatrics recommended in 2001 that parents limit screen use in children older than two to fewer than two hours a day and Australian health authorities adopted the guidelines.
Writing in the journal BMC Public Health, the Perth researchers said television was still the most popular screen choice but some children simultaneously used two or three devices.
Lead researcher Stephen Houghton said that though boys were more likely than girls to watch computer games for long periods, girls were the surprising big users of television, the internet and in particular social media.
"Specifically, by 15 years of age girls were almost seven times more likely to exceed the less-than-two-hours recommendation for social networking than boys," he said.
Professor Michael Rosenberg, of UWA's school of sport science, exercise and health, said that though the study's results might discourage parents trying to impose screen limits, they should not give up.
"The study shows that it's difficult but you still need to try to encourage kids to limit their screen use," he said.
"Even if you're not achieving the two-hour limit, you are not failing your kids.
"If you are putting rules in place that limit their screen use and encourage them to do physical activity, sit less and physically be with their friends, you're doing all right."
Professor Rosenberg said that though there were concerns about adverse physical and mental health outcomes from using screens, which were still being investigated, there were also potential benefits.