It's Earth Day! by Mercer Mayer.
Little Critter is on a mission! After a field trip to the recycling center and watching a film about
climate changes at school, Little Critter decides to do his part. He's going to reduce, reuse, and recycle. He's going to stop wasting water and energy. And he's going to build a climate control machine.
OR maybe you have a Fancy Nancy fan in your house. If so, check out Every day is Earth
Day by Jane O'Connor
After learning about conservation at school, Nancy tells her dad that he needs to take shorter showers: "Get clean, but stay green!" When she
ramps up the eco-enforcement, minor mishaps result. 
Lola Going Green by Christine Pakkala
Lola is tired of being last - which happens a lot when your surname starts with "z". So she wants to win the recycling prize with a project that will save the planet. She comes up with something that
can be done right in the classroom ~ something that will make a difference and has to do with slimy spinach.
And runaway worms.
If you're looking for something to do that will make a difference, try "going green" at home.
Green Clean by Linda Mason Hunter & Mikki Halpin offers chemical-free strategies for cleaning ~ with room-by-room chapters
on how to clean every place from under the kitchen sink to the shower
curtains. The authors include recipes for safe, simple, and economic
cleaning solutions plus their thoughts on the best eco-friendly cleaning products
on the market today. The book's even published in a waterproof and stain-resistant format for those who would want to keep a copy in a bucket with cleaning supplies without ruining it. And, the writers say, at the end of its life the book can be recycled. 
Just not the library's copy!
Energy island : how one community harnessed the wind and
changed their world by Allan Drummond is a true story about the small Danish island of Samsø. It became energy independent by shifting completely from fossil fuels to wind power and other renewable sources. The leader of this movement was a teacher who started his campaign by asking his student to "Imagine if we really
could make enough energy from the sun, and our crops, and even our own legs, to
power up the whole island!" It's a wonderful story, accompanied by factual sidebars that explain terms and make it an ideal book for older kids to read with younger children.
