I found it on youtube in a video illustrated with pictures of old Ireland. You may watch and listen here. Addendum: I just saw that you can't watch it on the blog, but must click the watch it on youtube button. Sorry for the extra step.
The faerys [sic] are luring a child to go away with them. They present their home as a beautiful place "where flapping herons wake the drowsy water rats." This is a place of dancing and joy "while the world is full of troubles and anxious in its sleep." And that last line of each verse is a killer - "for the world's more full of weeping than you can understand." The last verse tells of the good the child will be giving up to avoid the inevitable sadness in real life.
Oh, Yeats! A wonderful poem, and I do love the musical version and narration.