There is actually a lot to do in the Kingston Springs area.
Narrows of the Harpeth I always enjoy the walk not only to the falls side of the tunnel but also the overlooking bluffs. Moving water is always relaxing and peaceful. Also, the history of the tunnel is interesting.
Foggy Bottom Canoe and rent a canoe and spend hours on the river.
Adventureworks Zip Line Tours - zip lining is fun and is located in Narrows of the Harpeth. You will have to follow the signs.
There is a small water park for smaller children.
Great restaurants around.