Eleven activities for outdoor education for elementary grade students: http://www.plt.org/environmental-education-for-early-childhood. Scroll down to "Student Activities."
A homeschool family could easily incorporate one a month to expand your outdoor /environmental education activities.
Looking for PK or secondary? Try these links here: http://csfs.colostate.edu/pages/project-learning-tree.html#activity-guides
The easiest way to learn about the natural world is just to get out in it. Find a local trail, park, beach, or other habitat to explore, question, and fall in love with.