Too much time spent watching TV and playing computer games can hold back the development of young children, new research suggests.
A study of 2400 Canadian children found more screen time was linked to lower scores in "milestone" tests of communication, problem solving, interpersonal skills and physical co-ordination.
The amount of time two- and three-year-olds devoted to screen-gazing had a negative effect on their performance at three and five.
There was no evidence children with developmental problems were allowed more screen time by their parents to control challenging behaviour.
Writing in the journal Jama Pediatrics, the team of Canadian psychologists concluded: "The present study examined developmental outcomes during a critical period of growth and maturation, revealing that screen time can impinge on children's ability to develop optimally."
The effect of screen time on children is a hotly debated topic and so far the jury has been out on how significant an impact it has.
By the time they start school, a quarter of children show some degree of deficient or delayed development in language, communication, motor skills and "socio-emotional health", according to the team led by Dr Sheri Madigan from the University of Calgary.
To investigate the possible link between screen time and developmental delays, the scientists used a standard milestone screening measure that involved questioning parents about their children's abilities.
Higher levels of screen time at the ages of two and three years turned out to be "significantly associated" with poorer test results at three and five years.
The opposite association - poorer developmental progress leading to more screen time - was not observed.
The researchers pointed out that child development "unfolds rapidly in the first five years of life".
"When young children are observing screens, they may be missing important opportunities to practice and master interpersonal, motor and communication skills," they said.
The study found children watched screens for an average of 17.09 hours a week at age two, 24.99 at age three, and 10.85 at age five.
The authors urged health professionals to work with families to develop "personalised media plans" designed to place boundaries on children's screen time.
