Children who are obese are damaging their feet and may have problems walking, a study has suggested.
Obesity can affect children's feet as well as other aspects of their health
The research, presented to the Society of Podiatrists and Chiropodists conference, found obese children had wider and longer feet than normal.
Obese children were also found to have problems balancing, and walked at a slower pace.
Experts warned the effects of obesity put children at risk of long-term foot, leg and back problems.
Each foot is made up of 26 bones, around 19 muscles, a large number of ligaments, tendons, blood vessels and nerves and is designed to absorb the shock of walking and running.
But podiatrists say that excess weight and obesity can damage the delicate, immature nature of children's feet, leaving them at particular risk of deformities and abnormalities.
One study by the podiatrists looked at 200 children from Glasgow aged nine to12 years - 54 were obese and 15 were severely obese. Another 30 were overweight.
Obese children had feet that were up to 15 millimetres (mm) longer and seven wider than feet in normal weight children.
In children with severe obesity, their feet were on average 18mm longer and 15mm wider.
A second study of 44 nine to 11 year olds, half of whom were obese, found that the obese children were unstable when they walked.
They spent more time balancing on two feet when walking and less time on one foot than normal weight children. They also walked at a slower pace.
Flat feet can lead to other problems, such as knock-knees which can lead on to other knee problems and - later in life - to back and pelvis problems.
Some children are born with flatter than normal feet, and for them putting on too much weight can exacerbate the problems that can cause.
Others will be born with normal foot structures, but their weight will still cause problems.
Podiatrists suggest it can put extra pressure on the joints in the foot, leading to problems in the way the foot aligns and functions.
'Prevention better than cure'
Dr Stewart Morrison, a lecturer from the University of East London, who carried out the research, said: "Obese children are less stable when walking and cannot walk efficiently.
He added: "The findings are interesting because previous research suggested that foot problems limit obese children's ability to take part in physical activity - so encouraging them to carry out exercise might not be the best thing."
Gordon Watt, a consultant paediatric podiatrist, added: "This research is very important as it flags up to the podiatrist the 'at risk' nature of the foot in the child who is overweight or obese.
"Clinicians have been aware for some time of particular problems associated with these children but this research provides evidence that obesity and being overweight has an effect, not only on the development of the foot, but also on the way the foot and lower limb functions during walking."
Dr Ian Campbell of the charity Weight Concern said: "This typifies the problems of obesity, showing it affects every part of the body.
And he said that foot problems limiting the ability of obese children to exercise put them in a "catch 22 situation" because they need to be more active.
"This reinforces the need for prevention rather than cure, and for early intervention."