Parents should avoid letting their children use mobile phones, tablets or computers an hour before bedtime, according to new official guidance.

Experts say that looking at screens in that hour before bed can disrupt sleep and impact children’s health and wellbeing. And, spending long periods on the gadgets is associated with unhealthy eating and a lack of exercise.

Issuing the first official guidelines on screen time, the Royal College of Paediatrics and Child Health recommended time limits and a curfew, but said parents need not worry that using the devices is harmful in itself.

[Read More: Is screen time actually bad for your kids? Experts say probably not]

Parents are often told that gadgets can pose a risk to their children, but they can in fact be a valuable tool for children to explore the world, the college said.

Nevertheless, screen time should not replace healthy activities such as exercising, sleeping and spending time with family.

The college has drawn up four questions to help parents judge if their children are using screens in a healthy way:

:: Is your family’s screen time under control?

:: Does screen use interfere with what your family want to do?

:: Does screen use interfere with sleep?

:: Are you able to control snacking during screen time?

Dr Max Davie, the college’s officer for health promotion, said: “When it comes to screen time I think it is important to encourage parents to do what is right by their family. However, we know this is a grey area and parents want support and that’s why we have produced this guide.

“We suggest that age-appropriate boundaries are established, negotiated by parent and child that everyone in the family understands.

“When these boundaries are not respected, consequences need to be put in place. It is also important that adults in the family reflect on their own level of screen time in order to have a positive influence on younger members.”

How parents can judge healthy screen time

• Is your family’s screen time under control?

• Does screen use interfere with what your family want to do?

• Does screen use interfere with sleep?

• Are you able to control snacking during screen time?

The college recommended that screens are not used for an hour before bedtime due to evidence that the devices stimulate the brain, while the blue light they produce disrupts the body’s creation of the sleep hormone melatonin.

They also warned that watching screens can distract children from feeling full which, paired with advertising, can lead to higher intake of unhealthy foods.

The college issued the advice as a review published by the British Medical Journal found “considerable evidence” of an association between obesity and depression and higher levels of screen time. However it said evidence for impacts on other health issues was “largely weak or absent”.

“Given the rapid increase in screen use by children and young people internationally over the past decade, further research is urgently needed to understand the impact of the contexts and content of screen use on children and young people’s health and wellbeing, particularly in relationship to mobile digital devices,” the study authors said.