It is enough to make parents think twice before plonking their toddler down in front of Peppa Pig for too long.
A study has found every hour of daily television for a two-year-old could make them 16 per cent heavier as a teenager.
Very young children who spend too much time staring at a television screen are more likely to eat unhealthy food when they are older and do worse at school.
Researchers at the University of Montreal looked at nearly 2,000 children born two decades ago, whose parents reported their viewing times.
They suggest watching television as a toddler may lead to sedentary habits, while also exposing children to more junk food advertising at a young age. For every hour in front of the box when they were two, the 13-year-olds in the study ate 13 per cent more unhealthy food, which included soft drinks, sweet snacks and fast food.
Every hour of daily television for a toddler could make them 16 per cent heavier as a teenager
DOES WATCHING TELEVISION INCREASE CHILDREN'S RISK OF DEVELOPING DIABETES?
Watching television for three or more hours a day may increase a child's risk of developing type 2 diabetes, research suggested in July 2017.
Children who spend at least three hours in front of a screen are heavier and have greater insulin resistance, a study found. Both of these are risk factors for the condition.
Such youngsters also produce impaired amounts of the hormone leptin, the research adds. Leptin is involved in regulating appetite.
These results remained even after the study's participant's activity levels were taken into account, the study found.
Study author Dr Claire Nightingale from St George's, University of London, said: 'Our findings suggest that reducing screen time may be beneficial in reducing type 2 diabetes risk factors, in both boys and girls, from an early age.
'This is particularly relevant, given rising levels of type 2 diabetes, the early emergence of type 2 diabetes risk, and recent trends suggesting screen-related activities are increasing in childhood.'
The researchers analysed 4,495 children aged between nine and 10 years old.
The children were assessed for factors that influence their risk of developing diabetes.
Their body proportions, activity levels and the amount of time they spend in front of a screen - either watching television or using a computer - every day were also recorded.
'Watching TV is mentally and physically sedentary behaviour'
The study's lead author Isabelle Simonato said: 'Watching TV is mentally and physically sedentary behaviour because it does not require sustained effort.
'We hypothesized that when toddlers watch too much TV it encourages them to be sedentary, and if they learn to prefer effortless leisure activities at a very young age, they likely won't think much of non-leisure ones, like school, when they're older.'
Previous research has raised concerns about the effect of screen time in very young children, which can include sleeplessness and unhappiness.
The latest study asked children's parents how much television they watched aged two, and the children themselves about their diet aged 13.
The results suggest food adverts at a young age may have an effect, with children who watched television more likely to eat sweet and salty snacks, as well as French fries and desserts.
For every hour they spent watching television aged two, the teenagers had a body mass index (BMI) approximately 16 per cent higher. Children brought up in front of the screen may miss out on outdoor games and social interaction, the authors suggest.
The study, published in the journal Preventive Medicine, also found children who watched more television were more likely to skip breakfast and were less engaged at school.
'Rewarding distraction via entertainment will influence a young person's commitment to school'
Professor Linda Pagani, a co-author from the University of Montreal, said: 'In preschool, parents use screen time as a reward and as a distraction. They establish quiet 'idling' at a teachable moment when children could actually be learning self-control.
'Using distraction as a reward to help children behave in situations where they should be learning self-control sets them on a trajectory where they will seek out distraction when faced with demands for cognitive effort.
'Rewarding distraction and low mental effort via entertainment will later influence a young person's commitment to school and perseverance in their studies.'
Every hour in front of the television aged two was linked with a nine per cent decrease in teenagers' engagement with school.
There are no official guidelines for how much screen time children should have in the UK, but the American Academy of Pediatrics has reduced the amount of daily viewing from two hours a day to one a day for children between ages two and five.
Professor Pagani said: 'This study tells us that overindulgent lifestyle habits begin in early childhood and seem to persist throughout the life course.
'An effortless existence creates health risks. For our society that means a bigger health care burden associated with obesity and lack of cardiovascular fitness.'