Children who spend prolonged periods sitting - eating, doing homework, watching television, playing computer games - are at greater risk of long-term health problems, experts are warning. Among them are obesity, metabolic disorders and reduced bone density.

The good news is that for many daily activities, it's possible to cut down on sitting or even avoid it altogether.

"This is best done when the entire family gets involved," said Jens Bucksch, who works in the Department of Health Sciences at Germany's Bielefeld University and does research on prevention of health problems.

Homework, for example, doesn't have to be done in a sitting position. Children can stand while reading or writing.

"A lot of kids have a height-adjustable desk in their room," noted Bucksch, who recommends placing thick books under the legs of a desk that can't be raised high enough to work at comfortably while standing.

A child's room can also be equipped for jumping, climbing and swinging - for example with a mini-trampoline, ropes and cables, tubes and rope ladders.

In addition, all family members could agree to spend less time passively sitting. While watching television, for instance, they could stand up during commercials and walk around.

Instead of parents driving children to school or day-care centre, kids could take a bicycle or a young child's balance bike.

To motivate families to get more exercise, Bielefeld University even devised a downloadable game - points are awarded for time spent being physically active.

Although research on the health risks of prolonged sitting is incomplete, researchers say it's clear that exercise doesn't fully offset the bads from sitting down.

"Every hour of exercise is beneficial, of course," Bucksch said, but added that playing football for an hour didn't make up for spending the rest of the evening sitting in front of a video-game console.-dpa