It's fallen out of fashion with some parents, who’d rather negotiate with their children over bedtime.
But setting a strict deadline is the most effective way to make sure they get the best sleep, researchers found.
While simply "encouraging" youngsters to go to bed in the week might lead to fewer tantrums, it means they get less slumber than they need. A Canadian study of more than 1 600 parents found that children simply urged to head upstairs were 71 percent less likely to get an adequate nap. Those with specific bedtimes were 59 percent more likely to get the best quality shuteye.
Sleep deprivation appeared to rise as parents became less involved in bedtimes, with 15-year-olds worst affected.
The study by Public Health Ontario is based on recommendations of nine to 11 hours sleep for five to 13-year-olds, which is similar to British advice, and eight to 10 hours for those aged 14 to 17.
Children who are sleep-deprived are more likely to be obese and do more poorly at school, previous studies have claimed. Study author Dr Heather Manson said: "In the family context, parents’ support behaviours towards sleep could play an important role in their child’s health."
The study found weekend figures differed because parents tended to be less strict, allowing children to spend more time on smartphones and tablets in bed.