Handbook of Nature Study My basic go-to nature study resource (primarily for teacher reference).
Keeping a Nature Journal: Discover a Whole New Way of Seeing the World Around You Highly recommended by many. Lovely examples of what a nature journal *could* look like. May be overwhelming for the non-artsy or for a beginner...
James Herriot's Treasury for Children: Warm and Joyful Tales by the Author of All Creatures Great and Small Books like this one with stories about animals often inspire children to form relationships of their own with living things.
The Boy Who Drew Birds: A Story of John James Audubon (Outstanding Science Trade Books for Students K-12) This biography is geared toward younger children with its lovely illustrations.
John James Audubon Read biographies of naturalists (famous lovers of nature). Many like this one, may be most appropriate for teacher inspiration and education.
Last Child in the Woods: Saving Our Children From Nature-Deficit Disorder This book has a lot of important statistics and such on the importance of time spent outdoors, but may be kind of a heavy read for beginners.
Girls Who Looked Under Rocks: The Lives of Six Pioneering Naturalists Here's a free bio, both the author and subject were great naturalists.