More movement is possible outdoors than in.  Just is.

Kids need room to move.  As a movement advocate, kids need the kinds of large, open and varied expanses only the outdoors can accommodate. Running as fast as you can can't be done indoors. Neither can running uphill, in the tall grass, through a summer shower or over a snowy slope. And forget about climbing trees. Yet it's these exact kinds of diverse conditions and terrains young children need to build their bodies, challenge their abilities, learn to adapt, and develop self-assurance. Kids need these natural challenges, to stretch themselves to their fullest potential.

Nature fuels curiosity. Once kids do get outside, there it is... nature's endless treasure hunt of things large and small to fascinate the curious, inspire the imaginative, and humble us all. Like a small child, nature never stops growing and changing. And like a great teacher, nature always has something new to share. 

Nature needs kids. Some futurists predict the single, greatest challenge our children's generation will face is the environment -- climate change, alternative energy sources, clean air, clean water, fresh food supplies and the like. But if the futurists are correct, it’s hard to imagine how this next generation is going to save the environment if they haven’t actually spent much time in it. Children need to build up their knowledge and familiarity with nature in order to develop respect for it. And respect, along with resourcefulness, is what our planet is going to need from our children. So I say, best to start early.