Fewer than 20 per cent of children aged five to 15 eat the recommended five portions of fruit or vegetables a day, according to new research by the British Heart Foundation (BHF).
The charity says children’s hearts are being put at risk by poor lifestyles that include a lack of exercise and unhealthy eating.
Almost half of children in the same age group eat foods such as fizzy drinks, chocolate and sweets every day, the research found.
Lifestyle habits ‘unacceptable’
Around 39 per cent of girls and 43 per cent of boys drink a can of pop a day, which can contain around nine teaspoons of sugar.
Simon Gillespie, chief executive of the BHF, believes the results should encourage children and their parents to alter their dietary habits.
"These figures are a warning that many of our children are in grave danger of developing coronary heart disease in the future if they continue to live the same lifestyle.
"This is simply unacceptable," he said.
Sedentary behaviour the norm
Despite government initiatives to reduce the problem of childhood obesity, the report found many children do very little exercise and spend more time in front of the television.
Up to 85 per cent of girls and 73 per cent of boys aged 13 do less than one hour’s physical activity a day, which is the recommended minimum for their age group.
And almost three quarters of girls and boys said they watched at least two hours of television on a weekday.
At weekends, 23 per cent of boys and 25 per cent of girls said they watched at least six hours of television.
A third of children overweight
NHS figures show that a third of primary school children are overweight or obese.
To tackle the issue of poor eating and unhealthy lifestyles among many young people, the British Heart Foundation has launched a Hearty Lifestyle initiative which, among other things, will see dieticians advise obese children.
Gillespie said: "Through our new Hearty Lives projects we are committed to working with local communities to give young people most at risk of heart disease a healthier start in life.
"By ensuring children develop healthy habits now we can give them a fighting chance of avoiding serious ill-health in the future."
Some health insurance policies can reward you with vouchers or lower premiums for eating fresh fruit and getting plenty of exercise.