After the ubiquitous "De Colores," I'd guess that the traditional Mexican children's tune "Chocolate" is the Spanish-language song that appears most often in our kids music collection. Simple enough for preschoolers of any language + sugar = generations of children's music longevity!
Sonia de Los Santos included a nice rendition of the song on her album Mi Viaje: De Nuevo León to the New York Island, and now it's got an simple but artfully crafted video to match. The illustration is from Mexican-born illustrator Rafael Lopez, and if you and your family enjoyed de Los Santos' album, or Dan Zanes' music and overall family music aesthetic, y'all will dig this.
Sonia de Los Santos - "Chocolate" [YouTube]