Screen addiction is causing toddlers to lose delicate coordination skills such as those needed to tie their shoelaces, research suggests.
A study of 2,400 children found that more screen time was linked to lower scores in "milestone" tests of coordination, as well as communication, problem-solving and social skills.
The amount of time two and 3-year-olds devoted to screen-gazing had a negative effect on their performance at three and five.
Scientists behind the study said that staring at screens may be causing children to miss out on the chance to practise physical and intellectual skills.
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", the researchers said.
To investigate the possible link between screen time and developmental delays, the team at Calgary University in Canada used a standard milestone screening measure that involved questioning parents about their children's abilities.
Higher levels of screen time at two and three years old turned out to be "significantly associated" with poorer test results at three and five years old.
Dr Dillon Browne, a child psychologist, said: "The more screen time these children have, the less likely they are developing their fine motor skills through playing with toys, dressing dolls, doing art and things like that."
British experts said more research was needed but agreed that parents should be encouraged to promote healthy interactive behaviour in their children.
Dr Bernadka Dubicka, from the Royal College of Psychiatrists, said: "This is the first study to show that increased use of screen time in very young children can be associated with slower development.
"Parents should actively encourage their children to engage in a range of activities which promote development and give them as much face-to-face time as possible. Parents should also be aware of how much time they spend on screens in front of their children."