When outside be a role model!
"Do as I say, not as I do." This exhortation rarely works. You are the leader and the children will follow your example. Your attitude toward the environmnet will register clearly with them as you carefully preplace a log rolled over for investigation, or pick up trash left by people there before you.
How you feel about nature should and will come throught to the children - when you stop suddenly to listen to a favoirte birds song or pause to watch an ant laboring under a heavy load. Curiosity and caring are contagious!
Hands-On Nature: Information and Activities for Exploring the Envionrment with Children.