Well, my simplest song (blank verse, of course), I guess was:

"Little baby turkeys
Want a drink of water."

I don't recall the tune, though I know the tune my mom uses when she tells me about the song. (Its sort of a variation on that classic "Nyah, nyah, nyah, nyah, nyah.") Mom says I made up the "song" when I was not quite two, so I won't apologize for the primitive lyric. ;-D