The recommendation that children should not use the devices in the hour before bedtime comes because of evidence that they can harm sleep.

The devices stimulate the brain, and the blue light produced by them can disrupt the body's secretion of the sleep hormone melatonin.

While there are night modes on many phones, computers and tablets, there is no evidence these are effective, the college said.

Overall, it found the effect of screen time on children's health was small when considered next to other factors like sleep, physical activity, eating, bullying and poverty.

It said there was a lack of evidence that screen time is beneficial for health or wellbeing.

Its guidance recommends that families negotiate screen time limits with their children based on individual needs and how much it impacts on sleep, as well as physical and social activities.