On Wednesday, WHO announced that children under five years old should not spend more than one hour a day watching such devices. Less than that is better, officials say, and children under age one should not get any screen time at all.
"What we are cautioning on is over-use of those electronic screen times with young children," WHO expert Fiona Bull told reporters.
The new guidelines are somewhat similar to advice from the American Academy of Pediatrics. That group recommends children younger than 18 months should avoid screens other than video conferences over the internet. It says parents of children under age two should choose "high-quality programming" with educational value. Boys and girls should be able to watch the program with a parent and understand what they are seeing.
The guidelines say that children under five should also be physically active and get enough sleep to help develop good lifelong behaviors. This will help prevent diseases in later life.
"In this age group of under-5s, it is currently 40 million children around the world (who) are overweight. Of that (figure) 50 percent are in Africa and the southeast Asia region," Bull said. The Reuters news agency says that number represents 5.9 percent of all children worldwide.
Early childhood is a period of fast physical and mental development during which behaviors are formed and ways of doing things can be changed, noted WHO. Its guidelines come from evidence in hundreds of studies, many from Australia, Canada, South Africa and the United States.
"Sedentary behaviors, whether riding motorized transport rather than walking or cycling, sitting at a desk in school, watching TV or playing inactive screen-based games" are increasingly common, WHO said. It added that such behaviors have been linked to poor health.
Some groups said WHO's screen time guidelines failed to consider the possible benefits of electronic media.
Andrew Przybylski is director of research at the Oxford Internet Institute at the University of Oxford. He told the Associated Press that WHO's screen time advice deals too much with the amount of screen time. He said it fails to consider the quality of the material being watched or how it is being used.
"Not all screen time is created equal," said Przybylski.
Britain's Royal College of Paediatrics and Child Health said the study data available was too weak to permit its experts to set any measure for the best level of screen time.
Max Davie is the college's Officer for Health Improvement. He told the AP the restricted screen time limits suggested by WHO do not seem proportionate to the possible harm done.
WHO did not go into much detail about the possible harm caused by too much screen time. But the guidelines did note that lack of sleep in children has been linked with increases in extra fat as measured by body mass index.
Shorter periods spent sleeping has been linked with more time spent watching television and playing computer games, it added.
I'm Dorothy Gundy.