Responding to the OP who was talking about Cincinnati's Kings Island (which is not open year round, just April-Oct or something like that) and Hershey Park, it would be about an 8 hour drive between the two, but there are plenty of fun family things in Cincinnati within a 30min drive of Kings Island. Kings Island is about a 30 minute drive from downtown Cincinnati
Cincinnati Tourism Info:
http://www.cincinnatiusa.com/
Kings Island is a very thrill-ride oriented park. There is a childrens area (currently being converted to a Snoopy and Peanuts theme) and an area with classic rides, but mostly big coasters and such. KI has a lot of special events throughout their season, including concerts with big name bands. There is also a huge waterpark attached and that is included in the admission price to Kings Island
One Lodging option is the Great Wolf Lodge (Indoor Waterpark) which is literally a quarter of a mile from the park (but you'd still have to drive to the park as it's a very busy road)
Also nearby:
Coney Island Theme Park: a very classic-rides family oriented park, I'd recommend for kids in the 12 and under set especially. Very cheap, also has an attached waterpark (separate charge). Think bumper boats, scrambler, ferris wheel, bumper cars, that kind of thing. This is right next to Riverbend (a big concert Venue)
Monster MiniGolf: Indoor Blacklight Putt Putt Golf
Cincinnati Museum Center: Huge childrens Museum, Omnimax Theater, Natural History Museum (with a very cool walk-through cave)
Newport Aquarium (actually in Northern Kentucky but right across the river from downtown Cincy)
Underground Railroad Freedom Center Museum
Creation Museum (This is a very Christian oriented thing, so may not be right for your family, but as it's a popular attraction in the area I figured I'd include it on the list)
Sports Games: Hockey (Cyclones), Baseball (Reds), Football (Bengals)
Lots of parks with events going on in the summertime, esp Sawyer Park (on the riverfront in downtown)
Local foods to try: LaRosa's (pizza), Graeter's (ice cream), Skyline Chili and Gold Star Chili (Cincinnati Chili), Busken Bakery (awesome cookies/baked goods)
Movie Nights on Fountain Square Downtown (Big screen a la Times Square) where you can bring a blanket and snacks and watch a movie under the stars
(One heads up...Cincinnati is not a town with much public transportation, so be prepared to drive your own car or rent a car to get around)