KC Trails

I've convinced my brother and sil to take a ride with me on Friday. They both have old Trek bikes. They want to ride asphalt (The Katy trail is still mushy anyway) and I think it should be flat. My sil broke her ankle in November and still wears a brace. First ride for her so I think up to 5 miles should be enough. I don't know of any trails in Kansas City area, as I don't live there. It would be nice to be scenic and flat so that they enjoy it and want to do it again. Anyone have any ideas?