The U.S. Fish & Wildlife Service has created a nature study site for elementary-aged children. It's called Neighborhood Explorers, and the motto is "Let's Go Outside!"
Through games and activities, children can earn patches while "learning about and exploring nature in their own backyards." Children also have a chance to be a "Reporter," by reporting the nature in their own neighborhood.
You do not have to register to use the site or to earn patches, but you may register if you want the system to save your patches.