Increasing numbers of parents are sending their children to the gym or even hiring personal trainers to get them fit. The experts discuss whether this is a great quick exercise fix for kids - especially obese ones - or just an unnecessary waste of time and money, which could be potentially harmful.

In the past, children got all the exercise they needed from simply playing outside.

But today, increasing numbers of kids are getting their exercise at children's gyms, often instead of outdoor play.

While the number of youngsters using gyms has trebled over the last two years, some parents are going a step further and hiring personal trainers to sculpt their kids' puppy fat.

Shokk, Britain's biggest junior gym company, has installed nearly 60 junior gyms nationwide and is building another two a month, predominantly for local authorities.

There are thought to be at least 80 junior gyms in the UK, mainly catering for children aged eight and over, although there is at least one which caters for children as young as five.

The gyms, which may be increasing in popularity due to the rising numbers of obese children, contain kiddie-size equipment similar to that in adult gyms, although some are designed to work more than one muscle at a time, and give the body greater support than their full-size counterparts.

Shokk spokesman Kieran Murphy stresses that their gyms are designed to entertain children at the same time as giving them a workout.

He says the aim is not to convince kids that working out in a gym is the only way to exercise, but that activity of any kind should become a part of their lives. For that reason, Shokk gyms provide coaching and information on a variety of other activities, such as football and baseball.

"One consideration is that there aren't enough young people playing outside," Murphy says. "But kids need variety, and they benefit from as many activities and as much exercise as possible."

Shokk facilities - which will generally cost around £15 a month for membership - are increasingly interactive, and include activities such as the Target Wall, where kids hit lights with their hand, or a bat or ball.

"There aren't any real negatives to it," Murphy says. "Most parents would much rather their young person was in a facility doing structured exercise than standing on a corner drinking cider."

While that's undoubtedly true, child exercise expert Neil Armstrong, director of Exeter University's Children's Health and Exercise Research Centre, stresses that any such facility has to have specially-qualified staff to avoid injuries to immature joints and ligaments.

"Resistance work in a gym can be done safely by children, as long as the coach is very well-trained," he says.

"The experience has to be fun, otherwise children won't make it a part of their lives."

Developing basic motor skills is vital, he says, and this can be done simply by kicking or throwing a ball.

"The key is to promote children's active lifestyles, though we'd rather they were active as part of their everyday lives, by walking to school, riding bikes and so on.

"But if they go to a gym, the emphasis should be on fun - and parents should get the message across to their children that you don't just exercise when you go down the gym - they can get exercise just by walking up the stairs."