As someone with a career based on the outdoors, ecology is on my mind. A lot. And I try to pass what I know on to my children. A great book for introducing kids to ecology, and the knock-on effects that our actions have on our environment, is called
The Day They Parachuted Cats on Borneo by Charlotte Pomeranz.

Bad news: the book is out of print. Good news: your library probably has a copy. For more fun: I am giving away a couple of garden books over at studio g. Come by and check it out.