Another vote for Sleeping Bear Nat'l Lakeshore, probably because we've volunteered there and know how fantastic the whole area is. If you go, definitely take the gentle float trip down the Platte River across from the Platte River campground. It ends at an awesome beach.
Bottom line...you know your kids better than us. Would they go for lovely beaches, dune climbing, a ferry trip to South Manitou Island as a day trip, the float trip or just being kids in nature surroundings or would they go for the amusement park better?
