Planning trip with grandchildren 5-9

Planning a trip with grandchildren 5-9. Staying in a cabin in Jackson Township, Vinton County. I would like to go to Old Mans Cave and want suggestions of what other things to do. Is tubing down the river a good thing to do with a 5 year old! Would also like to see a waterfall with a shorter hike as 5 year old legs get tired, not to mention the grandmas legs! Any suggestions are appreciated.
Thank you in advance.