Memorable for the Right Reasons
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Whatever happens, I think your kids will remember this trip just because they're of the right age to remember things, and because they'll be with their dad for a week. I will say, though that the way to make it even more memorable is to make it about the destination and the things you do, rather than spending a large chunk of your time driving to get somewhere that you think will be more interesting. So, especially for a first trip, I'd hold off on anywhere that will take two days to drive to (and two days back) such as the Black Hills or Gulf or Atlantic Coasts. Concentrate instead on those destinations that you can get to in one day but that offer a host of 'day trips' for variety. Some examples would be the UP, setting up a base camp around say, Marquette MI. Within reach: Pictured Rocks and the Apostle Islands, Tahquamenon Falls State Park, the Soo Locks, Mackinac Island State Park, and Colonial Michilimackinac State Historical Park.
Another possibility would be the Big South Fork National River and Recreation Area in Kentucky within range of Mammoth Cave, the Great Smoky Mountains and Dollywood, Cumberland Gap National Historical Park, and the lakes of the TVA. Other places with similar characteristics that you might want to look at as possible destinations/base camps include the Ozarks, the Alleghenies of western Pennsylvania, the Niagara area (passports would be in order), or exploring the Mississippi by traveling the Great River Road.
AZBuck