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With the sort of technology now available, children are spending more time in front of a screen than ever.

And experts warn that even if youngsters get daily exercise, the increasing hours sat watching TV, playing computer games or surfing the internet could put them at a much higher risk of getting cancer in adult life.

Doctors fear long spells of inactivity while glued to a screen may lead to childhood obesity and the associated health dangers.

And they are now calling on parents to restrict the amount of time kids watch telly or play computer games to less than two hours a day and delay the age they start allowing toddlers to become viewers.

Experts have long been concerned about inactive children and obesity, but the World Cancer Research Fund has issued a fresh warning over kids who exercise and still turn to games and the TV.

The charity’s head of health information Kate Mendoza said: “People often assume sedentary behaviour is the same as physical inactivity.

"But someone can do the ­recommended amount of daily physical activity and still be sedentary.

"Children may well get plenty of physical activity at school through sports or playing but if they spend a lot of time sitting down at home they might develop habits which could increase their risk of diseases like cancer, heart disease and diabetes in the future.

"By reducing their sedentary time children will lessen their chances of becoming obese.”

Professor Mitch Blair of the Royal College of Paediatrics and Child Health, added: “Whether it’s mobile phones, games consoles, TVs or laptops, advances in technology mean children are exposed to screens for longer amounts of time than ever before.

“We are becoming increasingly concerned that this encourages a more sedentary ­lifestyle.

"There are some simple steps to help keep screen time in check such as limiting toddler exposure and keeping TVs and computers out of children’s bedrooms.

“We would also advise restricting prolonged periods of screen time and recommend less than two hours a day in total.”

Last year, children spent an average of 5.9 hours a day in front of the TV, a games console or a computer, according to figures from research agency Childwise.

The internet helped boost that figure.

A decade ago 21% of kids had never been online. Today, the number is down to just 1%.

Get them off the sofa and more active

Comment by Professor Stuart Biddle, sedentary behaviour expert from Loughborough University

The number of hours children spend sat in front of the TV each week should be cut.

But parents should also restrict how long they watch the screen for in one go.

It is not just about children watching too much TV without a break, it is also about them sitting down too long in a classroom or in front of a computer too long.

The problem is simply sitting down too much. Evidence is building that ­sedentary behaviour is bad for you.

It is important to get children outside more and to get them involved in pursuits that don’t involve sitting down.

They could also be more active at school.

Children are not going to drop dead simply because they are watching too much TV or watching for too long without a break, but they are storing up trouble for themselves later.

The important thing to stress is that sitting time is independent of how much exercise a child does.

Of course exercise is important, it must be done regularly and parents should continue to encourage this.

But that should not mean children can then spend hours on the sofa when they are back at home.

That is the same as adults playing sport and then having a cigarette afterwards.