More than two-thirds of children have a computer, games machine or TV in their bedroom and are losing out on sleep as a result, research suggests.
The poll of 1,000 parents also showed a fifth of young children get two to five hours less sleep a night than their parents did at that age.
Researchers at the University of Oxford said the long-term effects on child health were unknown.
Experts said bedtime routines are important.
Dr Luci Wiggs, research fellow at the Oxford child and adolescent psychiatry unit, said: "This is the first generation of children to face such a plethora of alternatives to going to sleep and the long-term consequences in terms of physical and mental health for both the child and their family can only be guessed at.
HOW TO GET A GOOD NIGHT'S SLEEP
"What we do know is that impaired sleep quality or quantity may compromise children's physical health, academic achievements and mental health."
She said one of the main problems of children using TVs, game machines and computers before going to sleep is that the activities are unstructured.
The research, carried out for drink manufacturer Horlicks, found nearly a third of parents believed their children had less of a bedtime routine than their generation. It looked at children aged between four and 10.
Dr Wiggs added: "Today's diversions are more easily achieved and stimulating to children, leaving parents with a problem. These days it appears that children do not go to bed to read, or be read, a bedtime story in a relaxed, calming environment."
Bedtime routines should include at least 15 minutes of calming activities, such as being read a story, she said. Going to bed at the same time every night is also important.
Prof Jim Horne, head of the sleep research centre at Loughborough University, agreed with the findings of the research.
He said: "It is an increasing problem that once upon a time bedrooms were for quiet reading and settling down, but they have now become places of excitement."
Prof Horne said a calming routine before bed was particularly important for young children.
He said mobile phones were also becoming a problem, with research showing children were spending time texting under the bed covers when they should be asleep.
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