any National Park site. they all have Junior Ranger programs which are great tools for the kids to learn about the site, at the end they get a junior ranger badge. you can also get them the National Park Passport so each site they visit they can get the passport stamped. We started both our kids (6yr & 2yr) with passports last year and the 6 yr does the ranger programs, he got 2 badges last year, and will be getting at least one this year. we plan out trips to include as many national park sites as we can.
any location can be educational, depending on how you approach it. an amusement park can be lessons in engineering on how the rides are built. a park can be lessons in nature...types of trees, types of rocks, types of animals, protecting nature.
if they are into nature look into the toy line "Backyard Safari" they are toys but also gear for exploring the outdoors. the stuff is inexpensive, basic pieces can be found at Walmart, Target, Toys R Us. More unique pieces can be found online. This could be something you get them as a gift then have the bring it on a trip so that you can use it to explore.
Good Sam Life Members. Camping with two young children in a 2007 Pilgrim fifth wheel (278BHSS) pulled with a 2002 F350.