Parents have been urged to encourage their children to do more exercise as researchers have revealed that youngsters who are more physically active have stronger bones.
A study carried out by scientists at Southampton University found children who did the most exercise had more robust skeletons.
They compared the average amount of physical activity of 200 four-year-olds with the strength of their bones.
Dr Nick Harvey, clinical lecturer at the MRC Epidemiology Resource Centre, and manager of the project said: "Evidence suggests that it is likely that the better your bones are when you are young, the better they will be when you are older.
"So more physical activity as a child could potentially mean stronger bones in old age."
The findings were presented at the National Osteoporosis Society (NOS) Conference in Edinburgh.
NOS spokeswoman Sarah Leyland said: "The decline in physical activity in children over the last decade is worrying and this piece of research shows that it could have a detrimental effect on the nation's bone health."
The society said parents should encourage their children to be more active and walk short distances instead of sitting in a buggy or watching TV.