In his 2005 book, Last Child in the Woods, Richard Louv defined Nature Deficit Disorder - the
lack of nature education and outdoor exposure.
Studies are not just showing that exercise done outdoors is better for kids than indoors (though any is better than none!) but also that when a child is connected with nature her performance in math, reading and science also improves.
Kill the proverbial two birds with one stone (but please don't literally kill any birds in the parks) with a trip to your local park. Check out fall recreation options at your local parks and rec department, and also see what the Washington State Department of Natural Resources has going on to help your children succeed in school and in life.