"The results show that there is a lasting influence of screen time, especially when children are two to five years old, when their brains are undergoing a period of tremendous development", Madigan said, according to TIME.
Experts recommended no screen time for newborns all the way to two-year-olds, and then only one hour per day for kids older than that.
"It is notable that screen time reduced both children's sleep even at this early age and reduced parents' reading to children, which we know is a strong predictor of positive child outcomes, such as higher IQ", said Gentile, who called the new study "strong" and "well-conducted".
Researchers found that greater amounts of screen time from ages 2 to 3 were associated with significantly poorer performance when their development was assessed at ages 3 and 5.
The United States National Library of Medicine found that most children of all ages spend between five and seven hours a day in front of a screen.
"Our study shows that preschool kids who get too much screen time, on video games, internet-connected devices, television screens, and other digital mediums are among those showing delays and deficits in learning by the time they enter school at the age of five". Mothers responded to the Ages and Stages Questionnaire Third Edition (ASQ-3), which examines a child's developmental progress in terms of communication, gross motor, fine motor, problem solving, and personal-social skills at 24, 36, and 60 months.
Shapiro says that the last question is particularly important, because increased screen time is tied to an increase in obesity rates.
The scientists added: "When young children are observing screens, they may be missing important opportunities to practice and master interpersonal, motor and communication skills".
While higher levels of screen time did predict poorer outcomes, the opposite pattern was not observed. "This study shows that, when used in excess, screen time can have consequences for children's development".
Researchers say limiting children's time with electronic devices isn't easy, but there are ways to do it. "We're living in busy modern times, and our attention is often pulled in numerous directions, resulting in less time for parenting", Dimitriu said. She said that, from her point of view, the new findings "actually support the AAP recommendations regarding screen time".
Is your family screen time under control?
Or were delayed children, who perhaps had more challenging behaviours, being plunked in front of screens more often to help them (and their parents) cope?
Glowinski compared the field to earlier research aimed at creating the healthiest meals for children.
Madigan encourages parents and guardians to set a good example and attempt to engage their children while they're watching the devices.
Spending time on a screen might cause kids to miss opportunities for learning. They recommend implementing a family media plan.
Dr Max Davie, from the Royal College of Paediatrics and Child Health (RCPCH), said: "We would, in the light of this paper, reiterate our advice that families spend time interacting as a family, that screens are not allowed to interfere with sleep, and that screen based interaction is no substitute for in person contact".