This light, folk-style round is based on the whole tone scale. (Discuss this scale with your students. Relate it to the "black keys on the piano.")
If you use the P/A cassette, you will hear that the song begins with the sounds of birds and gently flowing water. The sounds continue for the duration of the song, lending a serene quality and setting the tone for the singing.
Again, the guitar can be focused on easily. Two acoustic guitars in octaves and a mandolin are used for the continuing treble line. The only other instrument used is the piano, but you might want to consider adding autoharp to the blend.