When our kids were young (up until 10-12 years old), we kept trips relatively simple and fun. We mostly stayed at "resort" campgrounds with all the stuff - pools, mini golf, playscapes, etc. I would usually try to plan some sort of day trip to see something, but always kept in the back of my mind just staying at the campground if that seemed like the thing to do.
Early teens, then we started really hitting the historic areas and scenic areas. And... Disney World! I kinda lean towards Disney World really being for 10 years and up to really enjoy it. Certainly young kids have fun there, but ask any 20-something who went to Disney World as a 3 year old if they remember it.
"Must see" places... Really, there is usually a reason why someplace or thing is a "must see". Even if you only see it once (Niagara Falls sort of fits that for me).
Otherwise, as so many have posted, just camping with the family is worth it. Growing up, my family never camped. I am glad my kids have had the adventures we've had.
