Children's waistlines have expanded by two clothing sizes over the past 20 years, a new study shows.
Their waists have increased by about 4cm (1.57in) over the past two decades, reveals the research from the Archives of Disease in Childhood.
Researchers say the figures, which also show that girls are getting fatter quicker than boys, are proof of the alarming growth in child obesity in the UK.
Dr Mary Rudolf of East Leeds Primary Care Trust, says in today's British Medical Journal: "This figure is all the more disturbing when one reflects on how many notches on a belt this represents."
Waist size is seen as an important indicator because of the link between abnormal girth in adulthood and increased risk of heart disease. Researchers weighed and measured 500 children from 18 schools from 1996 to 2001, and compared the figures with past research.
In the final year, 315 children from the group, with an average age of 13, were examined and it was found their weight gain exceeded what would be expected against normal growth.
In 1996, one in 10 boys and one in eight girls were overweight; by 2001 one in seven boys and one in six girls were overweight. Waist sizes were also "significantly larger" than in 1996.
Dr Rudolf said: "The previous rise in body mass index levels reported through primary schools has continued into secondary school and emphasises the need for more rigorous efforts to stem the tide of child obesity."