I used to sing a Spanish version of this to my song in NY in the mid 1970s. I got it from a Mexican record for kids to sing along. I thoughy it was a Mexican llulaby. Forty years later I heard it in an episode of Foyle's war; a British TV show. A German WWII soldier was singing it while playing an accordion. It does seem to be a variation of Muss I denn, a German tune from the 1820s. Quite a distance from Mexican folk music!