Possibly Frere Jacques or one of the other French songs taught to me by my French great-grandmother when I was about three or four years old. Or maybe Itsy Bitsy Spider or one of the other childrens' songs taught to me in English by my parents.

First tune I ever played on the piano (my first instrument) was probably Frere Jacques or Mary Had a Little Lamb or something like that when I was about four. And I do consider these folk tunes and songs.