Owning a dog could help to lower the risk of childhood obesity, according to researchers.
A study of children in 78 inner-city primary schools in England found children in homes with dogs were more active than those without.
Researchers from St George's, University of London, were carrying out a study on child heart health.
They found that children in dog-owning families took part in more physical exercise and were less sedentary.
But researchers are still not sure whether this is a case of more active families being more likely to own a dog - or if owning a dog makes an otherwise sedentary family more active.
"It's a bit of a chicken and egg question. Long-term studies are needed to answer it, but it may be a bit of both," says Christopher Owen, senior lecturer in epidemiology at St George's.
The study measured levels of activity, such as the number of steps walked and time spent in light or moderate to vigorous physical activity, using a sample of more than 2,000 nine and 10-year-old children.
About one in 10 of these families, in London, Birmingham and Leicester, lived in a household with a dog.
It found a consistent picture for both boys and girls, on weekdays and weekends, that children in dog-owning families had a higher level of physical activity.
This could mean that children were accompanying their parents when walking the dog - or playing with the dog at home, rather than playing on the computer or watching television.
This increased activity could mean a significant difference for children's long-term health, says Dr Owen, reducing the risk of obesity or diabetes.
"It will confer a benefit on their health," he says.