Don Henley, formerly of the Eagles, founded the Walden Woods Project to protect a part of Walden Pond in 1990; this area was under the threat of real-estate development. A rather contemporary group involved in environmental issues might interest school children. In fact, newspapers recently featured Thoreau and his Walden Pond on the "Kids' Page."
Why use Walden in the elementary school? Thoreau's writing style is appropriate for the 4th or 5th grade level. There may be some challenging vocabulary, but it can become a part of the lesson plan.
What is your life interest? If it is conservation, you'll certainly find an ally in Thoreau. You might say he was the first person to advocate going "green." If it is economic conservatism, Thoreau has much to say about being frugal and spending money wisely as well. If it is living a healthy lifestyle, again, look no farther than Thoreau.
You can find the full text of Walden on eNotes at http://www.enotes.com/walden-text/. Read over it and I'm sure you'll find your own answer.
I am not sure exactly what you are asking, but Thoreau's work, Walden has many elements in it you can teach elementary school children. You could begin with recycling...in his section from Economy, he writes of working with nature and using only what one needs and how to survive off the land. In Solitude, Thoreau speaks of living alone, but not being lonely. He insists on being still and quiet in nature in order to think, to figure out who is he and how he fits into the big picture. A sort of "stop and smell the roses" idea, but more. He encourages thinking for oneself and not just following the herd...a great lesson on peer pressure. In Brute Neighbors, he watches the ants and compares them to the warriors in the Trojan war. A good biology lesson, or an introduction to mythology.
There is much here that can be brought down to an elementary level. You could also have them sit and write all they see, hear, smell, etc.--an excellent exercise in observation. They will probably be surprised how much they miss.
I have included a link I think you will find helpful.