"In the first few months, at least half of a child's sleep time is in a state equivalent to REM sleep," says Dr Paul Reading, neurology consultant at the sleep clinic at James Cook University Hospital in Middlesbrough, in the UK, and past president of the British Sleep Society.

“The majority of teenagers are probably a little sleep-deprived, partly because their clock mechanism makes it difficult for them to sleep at a conventional hour and then get up for school or work,” says Reading.

“The effects of sleep deprivation in children is difficult to study objectively but IQ, brain development and physical health all probably suffer. Also, children who snore very heavily are also generally stunted, probably because they lack a growth hormone that is secreted early in the night during the deepest non-REM sleep.”

According to clinical psychologist Dr Michael Breus, a fellow of the American Academy of Sleep Medicine, “Roughly 25 per cent of children with ADHD actually have an underlying sleep disorder. For those one in four children, when they get enough sleep, their problems go away.”

Prof Christian Cajochen, head of the centre for chronobiology at the University of Basel in Switzerland, says a multidisciplinary expert panel recently issued its new recommendations for appropriate sleep durations, which advocates wider appropriate sleep ranges for most age groups.

“What is nice about this is that it’s the first time that a professional organisation comes with age-specific recommended sleep durations built on a rigorous, systematic review of the world scientific literature relating sleep duration to health, performance and safety,” says Cajochen.

In summary, the panel recommended: Newborns (0-3 months): Sleep range narrowed to 14-17 hours each day (previously 12-18)

Infants (4-11 months): Sleep range widened two hours to 12-15 hours (previously 14-15)

Toddlers (1-2 years): Sleep range widened by one hour to 11-14 hours (previously 12-14)

Preschoolers (3-5): Sleep range widened by one hour to 10-13 hours (previously 11-13)

Children 6-13 years: Sleep range widened by one hour to 9-11 hours (previously 10-11)

Teenagers 14-17: Sleep range widened by one hour to 8-10 hours (previously 8.5-9.5)

Younger adults (18-25): Sleep range is 7-9 hours (new age category)

Adults (26-64): Sleep range did not change and remains 7-9 hours

Older adults (65+): Sleep range is 7-8 hours (new age category)