Many preschoolers in daycare may need more outdoor time to help increase their odds of getting enough physical activity, a small U.S. study suggests.

Pediatricians recommend that young children get at least an hour a day of physical activity to help build motor skills, coordination and strong muscles and bones, as well as to reduce the potential for obesity later in life. Playground time is also key for developing social skills like taking turns and conflict resolution.

But fewer than three in 10 children in full-time daycare got an hour outside for recess each day, the study found.

"It is ideal if parents can make some time for their child to play outside every day," lead study author Dr. Kristen Copeland of Cincinnati Children's Hospital Medical Center said by email. "But when children are in child care for eight to 10 hours, all of the daylight hours may be in child care settings, so this is not always possible."

Researchers studied 380 children ranging in age from three to six years old at 30 childcare centers from 2009 through 2011. In each center, they randomly selected two classrooms to observe for one school day.

On the observation day, researchers fitted children with activity trackers for a 24-hour period to record their movements in preschool as well as at home.

All but one of the daycare facilities had a playground outside and 23 had an indoor gym or activity space.

Just 14 of the centers had policies scheduling more than 60 minutes of daily outdoor time, however.

Only five centers had no television or computer use on either observation days.

While 90 percent of the daycare centers reported scheduling two or more outdoor sessions daily, only 40 percent of children participated.

The children who did get at least 60 minutes of outdoor or active time in school were also more active throughout the day, including time at home, than their peers who didn't get as much exercise in daycare.

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One drawback of the study is that it only included a single day of observation, the authors acknowledge in the American Journal of Preventive Medicine. It's also possible that even though researchers controlled for many factors that can influence activity levels in kids - including children's weight and parents' education levels - other variables may still have influenced the outcomes.

Even so, the findings suggest that parents should ask about physical activity policies when selecting a daycare center for their child, said Leigh Vanderloo, a pediatric activity researcher at the University of Western Ontario in Canada who wasn't involved in the study.

Ideally, the daycare should have access to quality indoor and outdoor activity spaces, limit screen time, and have policies in place to ensure that children get exercise even if the weather doesn't cooperate, Vanderloo said by email.

Expanding access to physical activity, however, isn't one size fits all, noted Laura Lessard, a researcher in behavioral health and nutrition at the University of Delaware who wasn't involved in the study.

In cities, it may not be feasible for daycare centers to have their own outdoor space, and nearby playgrounds might not be safe or appropriate for younger children, Lessard said by email. In suburban or rural areas, space may be abundant but kids might still lack access to enough play equipment or supervised physical activities.

"Internationally the childcare environment is predominantly a sedentary and obesogenic one," Vanderloo said. "It's important that we explore mechanisms to enhance the supportiveness and conduciveness of the childcare environment as it relates to physical activity, in addition to limiting the opportunities available to the children to engage in sedentary pursuits."