New government research shows that levels of childhood obesity have remained largely unchanged for the past decade.

For the first time since the mid 1990s, government scientists asked a large number of Australian children (4,400 between the ages of two and 16) about what they eat.

In a survey that also included questions about physical activity, CSIRO researchers found that while most children get enough exercise, time in front of television and computer screens has blown out dramatically.

The survey found 72 per cent of children are in the healthy weight range, but 17 per cent are overweight, 6 per cent are obese and 5 per cent are considered underweight.

The relatively unchanged levels of childhood obesity comes despite a common conception in today's society that Australian children are in the grip of an obesity epidemic.

"One of the surprising findings is that there hasn't been much of an increase," said Professor Tim Olds from the school of health sciences at the University of South Australia.

"In fact, it's pretty much plateaued over the last 10 years, the percentage of kids classified as overweight or obese, and that's encouraging news."

Less encouraging are the findings on the amount of time children spend watching TV and computer screens, what the survey calls 'screentime.'

"An average of almost four hours per day, and that doesn't include the time accumulated during school. And so they really were quite shocking to me," he said.

"I don't think it's good for kids to be doing anything for that amount of time, even if they're trying to find a cure for cancer or learning to play the Moonlight Sonata.

"I think to devote that much time when you're a child to one thing is a kind of distortion."

Physical activity

Despite Australia's children spending too much time staring at screens, the results on exercise levels are good. Sixty-nine per cent get the recommended one hour or more of moderate exercise per day.

But the group that reports doing the least amount of physical activity is teenage girls.

"If there's one group, which is the group of concern, it would be the older adolescent girls, the 14-16 year old girls, who show a really big drop off in physical activity," Professor Olds said.

Dr Jane Bowen from CSIRO Human Nutrition says the findings on the diets of teenage girls add to the concern.

She says 80 per cent of girls aged 14 to 16 don't consume enough calcium.

"Combined with low calcium intake, this group of girls has the least amount of physical activity, and they're both very important factors for bone health in girls."