For children under age 6, getting at least three hours of daily physical activity, spread out over the day, may be a good goal. Major organizations in three countries have now reached the conclusion that three hours of daily exercise should be recommended for children in this age group, the researchers said. The U.S. Institute of Medicine recommended those caring for children provide "opportunities for light, moderate, and vigorous physical activity for at least 15 minutes per hour," which translates to three hours daily, for children who spend 12 hours awake," published commentary in the journal Archives of Pediatrics & Adolescent Medicine. Obesity rates in 2- to 5-year-old children have increased dramatically since the 1970s, and currently, 26.7 percent of U.S. children of these ages are obese or overweight, the researchers said. Studies have not proved exactly how much physical activity is needed for young children to avoid obesity, though. "Clearly, it would be preferable to base a physical activity guideline for preschoolers on data linking physical activity to a health outcome, such as the development of body fatness," they said. Studies conducted using accelerometers (wrist watch-like device that measure physical activity) have shown that in preschool-age children activity is very sporadic, and very little of it is vigorous. In 2008, the U.S. federal government issued its first guidelines on physical activity, recommending 60 minutes of daily physical activity for children between ages 6 and 17, and 30 minutes daily for adults. Children under age 6 were not included in the recommendation. Pass it on: Kids under age 6 should aim to get three hours of physical activity daily.