sana sana colita de rana, que se alivie en la manana
healthy healthy tail of frog, which is relieved in the morning
heal heal toads/frogs tail may you heal in/by the morning
SOs mother used to sing this to SO and his siblings at night before they went to sleep.
SO told me that the toad/frogs tail is said in a cute sort of way. A way one would speak to a small child. The focus on a toad or frog as needing to be healed overnight perhaps comes from the fact that a frog lives its early life as a tadpole. Most markedly, the tadpoles tail disappears as it matures. While the song may have soothed the children to sleep, it also helps reassure their mother that when they mature (wake-up) they will be healthy (healed). It is as much a reassuring song for children as it is for parents.
A slight varitation on this lullaby can be found at: