We need our children to grow up to be fit and healthy adults, not just because it's what any civilised society would want for its children, but it's also best for our economy too," he added.
Dr Ann Hoskins, of Public Health England, agreed.
She said: "This study highlights that there is still much to do to keep children and young people active as they grow older, especially girls.
"The new school year is the perfect time to make healthy changes, swapping short car or bus journeys with walking or scooting to school.