I like this bluegrass band. I've had the album this song is on for quite a while and I keep coming back to it. I'm now listening to their latest album, which I bought today. The lineup has changed a bit since this video was made (they now have a different cellist and have added a fiddle player), but they still sound great.
Little Sadie is an old folk song. I've heard a few different versions of it over the years. Each one seems to have slightly different lyrics.