The world isn't about entertaining little kids and making them happy. Sure, they can get cranky if they don't get their way, but that is the fault of the parents. First, kids need to be taught to behave in all situations, and if they are bored, then just be quiet and patient. Parents today are too focused on making everything perfect for the kids at the expense of their own sanity. Having said that, there are great things to explore at every stop at the battlefield. The OP's kids are too young to understand the history and the military maneuvers, but they are old enough to look at the monuments and point out what they see and how each one is different. They are old enough to go through the museum and the cycloramic painting with things explained at their level. Many great museums around the world have programs just for kids. If a parent chooses to actually parent and teach, rather than just entertain, then Gettysburg will be a place the kids want to come back to.