The health benefits of eating fresh fruit and vegetables, particularly in averting cancer, will be extolled on Fruity Friday this week.
Children must be persuaded to eat more fruit and vegetables to prevent the onset of cancers when they get older, the World Cancer Research Fund said.
As many as four in five children are not eating the recommended amount of fruit and vegetables, the latest published Health Survey for England (HSE) for 2008 concluded.
And research by the Food Standards Agency, released earlier this year, showed that fewer than one in 10 teenagers are eating "five a day".
The HSE found that, on average, boys aged five to 15 eat 3.1 portions of fruit and vegetables per day, and girls consume 3.3.
One in 14 boys and one in 25 girls did not eat any at all on the day of the research.
Nathalie Winn, from the WCRF, said: "It is important that we encourage children to get into healthy habits as early in life as possible.
"This is because scientific research shows that eating a plant-based diet with plenty of fruits and vegetables, wholegrains and pulses probably reduces the risk of a number of types of cancer later in life."
Fruity Friday takes place on May 14 and is an annual initiative by WCRF to raise awareness of links between diet and cancer.