Children who do not have a regular bedtime are more likely to suffer behavioural problems.
Erratic bedtimes can cause a similar effect to jet lag and the longer youngsters go without regular bedtimes, the greater the impact on their behaviour, experts have found.
They believe going to bed at different times could disrupt natural body rhythms and cause sleep deprivation. In turn, this undermines the way the brain matures and the ability to regulate some behaviours.
But they also found the effect is reversible - parents who started putting their children to bed at consistent times noticed an improvement in their behaviour, as did teachers.
The study on more than 10,000 children was carried out by experts at University College London (UCL).
The data was collected via the UK Millennium Cohort Study, with bedtimes noted at age three, five and seven, and information on behaviour collected from parents and teachers.
Irregular bedtimes were most common at the age of three, when around one in five children went to bed at varying times.
However, by the age of seven, more than half of children went to bed regularly between 7.30pm and 8.30pm and just nine per cent went after 9pm.
The experts found that those youngsters who experienced erratic bedtimes throughout childhood displayed progressively worse behaviour.
But those children who went from varying bedtimes aged three or five to a regular bedtime by age seven displayed a notable improvement in behaviour.
Professor Yvonne Kelly, from UCL's department of epidemiology and public health, said: "Not having fixed bedtimes, accompanied by a constant sense of flux, induces a state of body and mind akin to jet lag and this matters for healthy development and daily functioning.
"We know that early child development has profound influences on health and wellbeing across the life course.
"It follows that disruptions to sleep, especially if they occur at key times in development, could have important lifelong impacts on health.
"What we've shown is that these effects build up incrementally over childhood, so that children who always had irregular bedtimes were worse off than those children who did have a regular bedtime at one or two of the ages when they were surveyed.
"But our findings suggest the effects are reversible. For example, children who change from not having to having regular bedtimes show improvements in their behaviour."
The types of behaviour studied included hyperactivity, repetitive bad behaviour, problems with peers and emotional difficulties.
Children whose bedtimes were irregular or who went to bed after 9pm came from more socially disadvantaged backgrounds.
They were more likely to have poor routines such as skipping breakfast, not being read to daily, having a TV in their bedroom and spending longer in front of a TV than children with earlier bedtimes.The research, published in the journal Pediatrics, said: "Family routines can be difficult to maintain when parents are working long, and potentially unsociable hours, thus policy development is needed to better support families to provide conditions in which young children can flourish."