My son (10 years old) and I did the zip line course in the morning, followed by rafting in the afternoon. GREAT experience. He was hesitant and nervous on the first zip line. By the end, he wanted to go first.
Guides are TERRIFIC. Wish I remembered the name of our (girl with a great sense of humor, and a guy who seemed to be an accomplished rock climber). All of them kept it fun and energetic.
Harpers Ferry is also a great town to visit. Make sure that you save time to check it out.