If you spend too much time looking around at screens, there is a risk that children will become short-sighted, become overweight, and get cancer, experts say.
A review of 80 studies on more than 200,000 people has ranked smartphones and tablets, along with sugary drinks, as one of the biggest risks to childhood obesity.
Overweight can lead to a dozen cancers, including breast, colon, kidney, liver, ovarian, pancreatic and prostate cancers.
The risk of dying young people increases too much time, which damages the eyes of young people – the number of short-sighted children has doubled in 50 years.
Researchers say the results are a "significant problem" and call for more control over junk food advertising, which worsens the impact of less active children.
Every additional hour a gadget day spends increases the risk of a child becoming short-sighted by three percent, as King's College London found out
The research of the World Cancer Research Fund investigated the causes of weight gain in children worldwide.
It turns out that the increasing time spent on smartphones, tablets and games is a big driver for kids getting fatter – and sugary drinks are the first two.
"The report highlights the importance of acting early to prevent cancer," said Sophia Lowes of Cancer Research UK to The Telegraph.
"Obese children are five times more likely to be obese than adults, which is worrying because they are at an increased risk for various cancers.
"That's why it's so important for us to see junk food ads on television at 9:00 pm and similar protection for kids watching ads on-demand and online."
Experts say not only that children do less exercise, but also when they look inward and look at screens.
They call this "passive overconsumption" – that is, children take snacks on junk food that are often advertised on the same devices they spend their time on.
In addition to obesity and cancer risks, too much time spent in front of monitors increases the number of children with myopia (short-sightedness).
The proportion of children with myopia worldwide has more than doubled in the last 40 years from 7.2 percent to 16.4 percent.
This effect has been termed "digital myopia". In a separate study, researchers at King's College London found that every hour and every day they spent using equipment was three percent more likely to cause a child's visual impairment.
Previous research has found that children spend an average of eight hours a day on gadgets.
Professor Chris Hammond of King's College told The Telegraph: "I think it's a big problem.
"We believe that young children staying in the house and spending hours on screens are bad for sight, not to mention obesity and fitness.
"I think our concept in myopia is clear that close work is a risk factor and that outdoor activities provide protection."
The eye expert Dr. Mohamed Dirani wrote in the British Journal of Opthamology: "The age of smart device adoption is getting younger and younger as many two-year-olds spend up to two hours a day using equipment.
"The use and misuse of smart devices, especially in our pediatric population, needs to be closely monitored to address the emerging phenomenon of digital myopia."
CHILDREN BORN IN SUMMER ARE DOUBLE WELL-BEING TO BE SCRENCHED
Children born in summer are almost twice as likely to be short-sighted as children born in autumn, winter or spring, scientists have found.
Researchers at King's College London tracked down 2,000 children born between 1994 and 1996.
By the age of 17, a quarter of participants had developed myopia – the medical term for myopia.
Those born in the summer semester were 93% more likely to be short-sighted than those born the rest of the year.
The researchers, whose study was published in the British Journal of Ophthalmology, believe that this is due to the fact that children born in the summer go to school earlier than other children.
This means that they start reading, writing, and other books earlier than other children before their eyes go out.
The authors wrote: In the UK, children start school in September of the academic year when they turn five.
"Therefore, those born in the summer could be almost a full calendar year younger than those born in the fall.
"In this study, children who entered the education system at a younger age – born in the summer months – had the highest myopathy chances.
Previous studies in Finnish, Israeli, British and American populations also showed increased myopia in summer births.
"We … suggest that the club may be due to an early confrontation with the education system." The researchers also found that children who spend hours playing computer games in their teens need glasses.
But surprisingly, infants born as a result of fertility treatment appeared to be protected against myopia, with IVF-born children 37 percent less short-sighted.