More than one third of US children are now overweight or obese, and the reason for the burgeoning bulge isn’t surprising — they aren’t getting enough exercise. But some of the causes of their sedentary habits are more startling, and go beyond the emergence of computers and social media that keep youngsters indoors and relatively immobile.

About 75% of preschoolers in the US spend most of their days in child care centers, and they’re not moving around for 70% to 83% of their hours there; in fact, they’re only active about 2% to 3% of the time. Why? Given the growing problem of obesity among children, why aren’t day care facilities focused on getting kids moving?

Dr. Kristen Copeland, a pediatrician at Cincinnati Children’s Hospital Medical Center, and her colleagues have been conducting a series of focus group studies exploring just that. In previous studies in which parents, teachers and administrators were asked about daily day care activities, they identified familiar issues such as clothing, weather and parental concerns as barriers to getting kids outdoors to play.

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In the current study, published in the journal Pediatrics, the team focused on societal factors that could make it difficult to maintain physical activity programs. After conducting nine focus groups with 49 child care providers in Cincinnati, Ohio, the team found three main societal barriers to exercise — concerns about the children injuring themselves while at play, financial constraints that limited some centers’ ability to purchase playground equipment, and a growing emphasis on academic learning over unstructured physical play time.

These factors are curtailing children’s natural desire to be active, says Copeland, and could be detrimental to youngsters’ health in the long term. “Children are naturally active — they love to play, and to play vigorously,” she says. “If given the time and place and freedom to run, they will do that. But children at this age are entirely dependent on caregivers for the opportunity to be active.”

Allowing children to be physically active from younger ages could help them to learn better and develop enhanced social skills as well. And rather than trying to convince sedentary older kids to start exercising, it might be more effective to establish exercise as a good habit at an early age. “Children develop mastery of gross motor skills — climbing, throwing and catching ball, skipping and learning to control their body — on their own at an early age, and these skills aren’t taught in school,” says Copeland. “And children who are most comfortable with these skills show more self confidence and have better peer relationships than children who don’t.”

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But caregivers cited some very real constraints in letting children play vigorously. For one, worries about injuries led many to limit play time and the types of physical activity children enjoyed; some parents of children in the study specifically requested that their children not be allowed to use playground equipment for fear they would get hurt. Parents also pressured some teachers of preschoolers to focus more on academic learning — of letters, numbers, shapes and colors — over physical skills such as climbing or skipping. “The question is, are we doing more harm to prevent scrapes by keeping children sedentary and letting them potentially become obese?” says Copeland.

While the focus group study was designed only to tease out what factors might be contributing to children’s inactivity, the teachers and caregivers also acknowledged that active time did not need to come at the expense of learning. Playgrounds are rich sources of learning, and children can become familiar with numbers, nature and concepts such as weather, time and distance with games organized around running or other playground equipment. But appreciating that exercise, which is often perceived as play time, can be an important partner to learning may take some time.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny . You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.