Inactive mothers may be preventing their children getting enough exercise by setting a bad example, a study suggests.
Scientists who measured the physical activity levels of mothers and their four-year-old children found a direct association between the two.
"The more activity a mother did, the more active was her child," said lead researcher Kathryn Hesketh, from University College London.
"For every minute of moderate-to-vigorous activity a mother engaged in, her child was more likely to engage in 10 per cent more of the same level of activity.
"If a mother was one hour less sedentary per day, her child may have spent 10 minutes less sedentary per day."
The study included 554 mothers, many of whom worked and had children who attended day-care facilities.
Both mothers and children were fitted with movement and heart-rate monitors that recorded their activity levels for up to a week.
Just 53 per cent of the mothers taking part in the study engaged in 30 minutes of moderate-to-vigorous activity at least once a week, the results published in the journal Pediatrics showed.
Government health guidelines recommend 150 minutes of "moderate intensity physical activity" such as brisk walking over the course of a week.
New parents are known to be less active than their childless peers. Once women become mothers, their activity levels frequently fail to return to pre-parenthood levels.
"There are many competing priorities for new parents and making time to be active may not always be top of the list," Ms Hesketh said.
"If activity in mothers and children can be encouraged or incorporated into daily activities, so that more time is spent moving, activity levels are likely to increase in both."