While parents may be increasingly worrying about childhood obesity, they must ensure their offspring eat enough fat, research from the US urges.
Cucumber is simply not enough, the research warns
Concerns about their child becoming overweight means some parents put them on low-fat diets, but the Nutrition Journal study said this was misguided.
Researchers found children burned substantially more fat than adults relative to their calorie intake.
Youngsters needed that fat to grow and thrive, they argued.
Over a third of a child's energy intake should be made up of fat, the researchers at Pennsylvania State University said, a recommendation in line with UK requirements.
"Despite this, many parents and children restrict fat for health reasons," they said. "Sufficient fat must be included in the diet for children to support normal growth and development."
All of the participants - 10 children and 10 adults - were put on the same diet, adjusted to estimated calorie requirements of each one.
During testing, none of the group led an active lifestyle. They spent their time watching films, reading, and taking occasional slow walks.
While the children did not use up more fat than adults in total, they burned up substantially more relative to the amount of energy they used, despite all participants' sedentary lifestyle.
UK nutritionists stressed fat, as much as possible, should come from "healthy" sources such as oily fish, while chips and crisps should be cooked in olive or sunflower oil.
"Too much saturated fat in the diet, e.g. from cakes, biscuits, pastries and fatty meats, should be avoided," said Claire Williamson of the British Nutrition Foundation.
The National Obesity Forum welcomed the study.
"I think this research is absolutely right," said board member Tam Fry. "Young children need more fat and energy for the whole purpose of growing and living.
"To give them low-fat and sugar-free products is a bad idea."
Tracy Kelly, of the charity Diabetes UK said: "A healthy, balanced diet should include fat.
"However, a diet high in fat, particularly saturated and trans fats, should be avoided.
"The spiralling rates of type 2 diabetes in children, a condition which traditionally affected people in middle age, are strongly linked to poor diets high in fat, sugar and salt."