The Old Blind Dogs seem to have learned the song from a Pentangle record, but without the benefit of the lyric insert that came with my copy. Pentangle set a Cruel Sister text to a Riddles Wisely Expounded tune and also borrowed the refrain from it; the song had not previously been sung to that tune,or with that refrain, so far as can be told. Bairn is a mis-hearing on somebody's part for Bent. The subject has been dealt with here at considerable length several times in the past.