I recently discovered on Mark Evanier's site as linked from Cartoon Brew a couple of UPA animated holiday shorts that are on YouTube. One was Peter Cottontail which for some reason is not listed on IMDb. That one played the whole song and depicted visually the entire premise down to the hunter that shot the rabbit's tail. This one, Frosty the Snowman, features the title character's fun with some kids before he leaves so he won't melt away. Both had a chorus that featured no musical accompaniment, just them singing in the standard jazzy style of the period. These were longtime annual staples on Chicago kid shows for years. As a longtime animation fan, these were pleasant surprises. Definitely worth a look.