Children who spend hours staring at screens every day are more badly behaved by the time they are five, a study has claimed.
The screen time has a ‘significant impact’ on the child’s development, researchers said as they warned parents need to cut it down.
One author of the study suggested this is because time spent looking at screens is time taken away from healthier activities such as sport or sleep.
But experts in the field immediately dismissed the findings as having ‘critical shortcomings’ and doing nothing to prove the screen time had actually caused the bad behaviour.
Scientists at the University of Alberta studied more than 2,400 families and found children glued to screens have more significant behavioural problems.
As well as a higher risk of attention deficit hyperactivity disorder (ADHD), those exceeding two hours per day were five times more likely to be inattentive.
‘We found screen time had a significant impact at five years of age,’ said Dr Piush Mandhane.
Three-year-olds in the study spent an hour-and-a-half, on average, looking at screens every day. This fell slightly to 1.4 hours for five-year-olds.
The researchers found screen time may even have a bigger effect on a child’s behaviour than how much sleep they get or how stressed their parents are.
And this may be because it takes away from other aspects of life which could reduce the risk of attention problems.
Dr Mandhane told MailOnline: ‘Our data suggests that more screen-time leads to less sleep-time.
‘Developing a regular sleep routine, consistent wake and bed times that limit screen-time prior to bed, in also an important part of growth, development, and behaviour.
‘In another analysis, we found that children who watched more than 2 hours of screen time per day were almost 65 per cent less likely to sleep 10 hours per day. So more screen time equals less sleep time.’
The study backs up past research also suggesting damage to sleep, and other studies pointing to poorer brain development, mental health issues and damaged eyes.
A lack of sleep in childhood could stunt the growth of the brain and therefore lead to problems later in life.
Scientists at the CHEO Research Institute in Ottawa found children aged between eight and 11 had five per cent worse brain function than their peers if they spent more than two hours per day looking at a screen.
This, they believe, could be because games and videos don’t stimulate the brain in the same way as, for example, reading a book.
It was also likely to mean they didn’t sleep as well as others.
In the research published today, the scientists found organised sport and sleeping well could actually protect brains from the bad effects of excess screen time.
They found the exercise itself was less important for improving the children’s behaviour than the taking part in arranged activities.
Dr Tamana added: ‘The more time children spent doing organised sports, the less likely they were to exhibit behavioural problems.
‘A lot of the things that you do through organised activities are really important for young kids early on.
‘I think in lieu of screen time, it would be beneficial for parents to increase opportunities for other structured activities instead.’
While the researchers suggested ‘less is more’, they didn’t recommend cutting it out completely.
Instead, they said, it is a good opportunity to make sure children use electronic devices sensibly.
‘Our data suggests that between zero and 30 minutes a day is the optimal amount of screen time,’ said Professor Mandhane.
‘The preschool period is an ideal time for education on healthy relationships with screens.’
Scientists in the UK have criticised the study and said it does not directly link screen time to bad behaviour or ADHD.
And they added the researchers overstepped the mark in issuing advice to parents and doctors based on a flawed paper.
Professor Andrew Przybylski, director of research at Oxford University’s Internet Institute, said: ‘There is no baseline data on children’s behaviour so it is possible that children who are predisposed to behavioural problems are also predisposed to higher levels of screen-time. The paper does not contextualise this properly.
He added: ‘The authors go well beyond their results in providing advice for physicians and educators. The correlations are very small and inconsistent.
‘It is mildly shocking the authors would promote limiting screen-time on the basis of these findings given the evidence in the paper suggests nearly every other factor analysed was a much stronger predictor.’
Dr Bob Patton, a lecturer in clinical psychology at the University of Surrey, said: ‘While [the study] suggests that children under the age of five who spend an average of two hours or more a day in front of screens are more likely to have an ADHD diagnosis, it does not provide any indication that screen time has caused the issues.
‘Whilst overuse of the “electronic babysitter” may or may not contribute towards the development of behavioural problems, parents should be mindful of the possibility, and ensure that young children participate in a variety of activities, both on and off screen.’
The research was published in the journal PLOS ONE.