The WHO drew on emerging - but as yet unsettled - science about the risks screens pose to the development of young minds at a time when surveys show children are spending increasing amounts of time watching smartphones and other mobile devices.
"Improving physical activity, reducing sedentary time and ensuring quality sleep in young children will improve their physical, mental health and wellbeing, and help prevent childhood obesity and associated diseases later in life", said Fiona Bull, programme manager for surveillance and population-based prevention of noncommunicable diseases, at WHO.
Limiting, and in some cases eliminating, screen time for children under the age of 5 will result in healthier adults, said World Health Organization, adding that quality sedentary time spent in interactive non-screen-based activities with a caregiver, such as reading, storytelling, singing and puzzles, is very important for child development.
The agency said infants less than 1 year should spend at least half an hour every day on their stomachs and that older kids should get at least three hours of physical activity every day.
Being inactive is a "leading risk factor" for mortality which fuels a global rise in overweight and obesity, the agency said.
Children aged over five are advised by the World Health Organization to be active for an hour a day but there had previously been no guidance for younger children.
Even at 1-2 years, though, screen time remains anathema.
Similarly, the American Academy of Pediatricsguidelines also recommend no screen time for children under the age of two, other than video chats like FaceTime, for example. Is WHO's recommendation sensible or unrealistic?
The guidelines also recommend that these children spend at least 180 minutes a day in a variety of physical activities. "What we really need to do is bring back play for children".
Have 11-14 hours of good quality sleep, including naps, with regular sleep and wake-up times.
WHO's screen time advice "overly focuses on quantity of screen time and fails to consider the content and context of use", said Andrew Przybylski, director of research at the Oxford Internet Institute at the University of Oxford.
Some fear that too much screen time reduces the time kids spent connecting and engaging with their caregivers, which is seen as crucial for their social and emotional development.
"It induces a real conflict", said University of MI pediatrician Jenny Radesky, author of screen-time guidelines for the American Academy of Pediatrics in 2016.
In Canada, screen time for children younger than two is not recommended.
Children shouldn't be restrained in a pram or high chair, or strapped to someone's back, for more than an hour at a time.
"Not all screen time is created equal", he added, urging further study on the various types of screen-based activities available to children and their impacts.
One in five children in England are overweight or obese by the time they start primary school, rising to one in three by the time they leave.
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