“Screen time” is a term used for activities done in front of a screen, such as watching TV, working on a computer, or playing video games. Screen time is sedentary activity, meaning you are being physically inactive while sitting down. Very little energy is used during screen time.

The amount of time children spend glued to a screen has risen dramatically in the last 20 years, a new report suggests. Children aged five to 16 spend an average of six and a half hours a day in front of a screen compared with around three hours in 1995, according to market research firm Childwise. Teenage boys spend the longest, with an average of eight hours. Eight-year-old girls spend the least – three-and-a-half hours, according to the study.

The reason behind all this gadget use: over a third of parents (35 percent) said they use tech gadgets to entertain their children because they are convenient, and nearly a quarter (23 percent) because they want their children to be tech-savvy. A 2015 survey of 1,000 British mothers of children aged 2 to 12 found that 85 percent of mums admit to using technology to keep the kids occupied while they get on with other activities. The AO.com survey pointed to children spending on average around 17 hours a week in front of a screen – almost double the 8.8 weekly hours spent playing outside. TV has been an easy “babysitter” for years now, aided even further with DVDs, and so on.

By the age of seven the average child will have spent a full year of 24-hour days watching recreational screen media, claims Sigman. Over the course of childhood, children spend more time watching TV than they spend in school. In a 2012 report on media consumption in the UK Ofcom estimated that the average 3-4-year-old spends three hours a day in front of a screen. This rises to four hours for ages 5-7, 4.5 hours by ages 8-11, and 6.5 hours for teenagers.

“Early screen viewing is likely to lead to long periods of viewing for the rest of your life,” says Sigman. “The way you view screens when you are young forms the habits you pick up for ever after it seems.” Like other addictions screen time creates significant changes in brain chemistry – most notably, in the release of dopamine. “Dopamine is produced when we see something that is interesting or new, but it also has a second function. Dopamine is also the neurochemical involved in most addictions – it’s the reward chemical.

“Computer game addicts or gamblers show reduced dopamine response to stimuli associated with their addiction presumably due to sensitization.”

Games in a virtual world also lead to a false sense of competence. Children need to base their lives on reality not fake, virtual worlds, says Sigman.

Fast use of a games console controller is of little use outside of the gaming environment. And the reduction in sustained attention is a far greater loss.

So how much screen time for children?

The simple answer: not much. None for children under two. That’s right. The experts suggest that babies and toddlers are kept away from all screens.

Children aged 2-5 years should have no more than an hour a day, and children aged 5-18 years should have no more than two hours a day. That’s a tough call for teenagers, especially with homework often requiring computer time. But remember that the real danger is non-educational, leisure screen time, so you may wish to discount homework screen time.

Parents should be able to decide if these strictures are too harsh, and allow some screen time flexibility, but not caring at all about the amount of time your children spend in front of screens is dangerous.