The National Parks Service has a wonderful Education program. They have a Junior Rangers program, a WebRangers program and Parks as Classrooms. Here is a list of parks that you can check out to see if you have one near you. Some parks even have curriculum based education programs.
Since we live near the Great Smoky Mountain National Park, we like to participate in their Parks as Classrooms Programs. They offer programs from Kindergartners up to the Eight Grade. Some of the 8th grade programs have been designed to meet the Standard North Carolina Course of Study for Biology and Earth Sciences.
A couple of years ago, my older kids participated in a program at Deep Creek. They had a Ranger talk with them about the different animals that live around the creek and how they survive. They loved the hands on approach of learning about animal habitats in the Mountains. We have also gotten the Junior Ranger workbooks and have worked in them with our 2 older children.
Be sure to do a search of the National Parks and see if there are any programs near you. I can guarantee that not only will you enjoy it, your children will too.