A new Scottish Government campaign, Take Life On, is aimed at informing parents of the health benefits of children participating in 60 minutes of physical activity a day.
It was launched by former international footballer Andy Walker, child development expert Sue Palmer and 60 pupils from Ruchill Primary in Glasgow.
Ms Palmer said: "If we left it to nature, there would be no problem keeping kids active. They are born to be active - running, jumping, sliding, climbing, generally making a lot of mess and noise. It's called playing. Unfortunately, over the past 20 years, we have got frightened of letting our children out to play.
"It's important not just for physical fitness, but for learning to get along with other kids, developing self-reliance and resilience, finding out about the world at first-hand and turning a child into a well-rounded, confident individual."
Research shows considerable variation in children's participation in physical activity (including school-based activity) by age and sex. Among boys in 2008-09, activity levels were highest between the ages of five and 12, when about eight in 10 met the recommended levels, falling to 70 per cent of boys aged 13 to 15. Among girls, levels of participation tailed off earlier and more sharply - from 79 per cent of girls aged eight to 10, to 67 per cent aged 11 to 12 and 41 per cent of girls aged 13 to 15.