Rocky Mountain National Park in Colorado (Stay right outside in Estes Park) would be a great national park experieince for you that would be easier to get too (a great alternative to Yellowstone). It happens to be my very favorite national park -- tons to do to keep you occupied for a week. Beautiful, lots of wildlife (not the variety of wildlife that is at Yellowstone and the Grand Tetons, but very good), beautiful family friendly hikes, great family ranger programs that are free and easy to get too -- less driving to get to where you want to be here, and a friendly town that is very close to the National Park, Estes Park with shops, resturants, kid activities. I do love Yellowstone, but actually prefer this park to Yellowstone as I spend less time driving and more time outside of my car in this awesome pristine natural place.