Half of seven-year-olds spend more than six hours a day sitting down and are failing to get enough exercise, a study indicates, according to a report in The Times.
Girls are much less active than boys, with only 38% as active as they should be, compared with 63% of boys, the research found.
Children of all classes needed to move more, with those from Asian backgrounds particularly inactive, scientists said.
The findings prompted warnings of a future full of health problems after a report last week warned that today’s generation of children were in danger of dying younger than their parents.
The study looked at 6,500 children from the Millennium Cohort Study, a sample of those born between 2000 and 2002. They wore movement monitors for a week, taking them off only when washing or sleeping.
In an average day the children took 10,229 steps but spent 6.4 hours in sedentary activities such as lessons or watching TV, results in the journal BMJ Open show. Only 51% got the recommended hour of daily physical activity.
This fell to 34% in those from Bangladeshi backgrounds, while children of Indian origin moved least, averaging 8,699 steps a day. In Northern Ireland 43% got enough exercise, rising to 53 per cent in Scotland.
The findings were recorded before last year’s Olympic Games, but the authors warn that much more needs to be done to capitalise on the legacy of London 2012.
Professor Carol Dezateux of the University College London Institute for Child Health, who led the research, said the “huge gap” between between girls and boys was “depressingly present from an early age”.
She added: “There are big gender differences around playground time. We need to look at how to get girls more into ball games, playground activities and activities such as dancing that are very good and may be more attractive to them.”
She recommended policies to promote walking to school, including safer streets and flexible hours for parents, as well as better parks and more sport.