PP is correct about the area around Nemacolin, but that resort is pricey and there are other options in the Laurel Highlands. We have rented a house through VRBO in the area and camped many times.
Your kids are too young for a rafting trip down the main part of the Youghiogheny (middle) which is class III+, but when my youngest was 6, we did a float trip down the Middle Youghiogheny and had a great time. http://wilderness-voyageurs.com/family.html
And yes, there is also zip lining and lots of other activities. My husband just had my 10 y.o. daughter out there for her first try at whitewater kayak school and they had a great time. They had classes daily, but also took time for zip lining, fishing and biking on the rail trail. www.laurelhighlands.com/activities/Zipline
Also, my kids really enjoyed the Falling Water house tour. They were 9 and 11, so use your own judgement with your 6 y.o.
Have you visited Cleveland? My kids enjoy the Metropark Zoo, the Great Lake Science Center, and the Cleveland Museum of Natural History. My husband has family there and I wasn't sure what a visit would be like, but I was very pleasantly surprised. We had visited the Rock n Roll Hall of Fame years ago, and didn't think it was worth the admission price, but some families really enjoy it as well.