I learned this one while on my mission. It is a good way to practice the erre sound which is the double R but sometimes shows up without the double R but at the beginning of a word. The erre sound is like that a child makes for a truck.
Erre con erre guitarra
Erre con erre barril
Rápido corren los carros,
[cargados de azucar] del ferrocarril.
Erre like the erre in guitar; Erre like the erre in barrel, rapidly run the trains loaded with sugar, of the railroad.
I learned this without the bit about sugar.
https://www.youtube.com/watch?v=piU9CAoOrGg