Happy Pig Day by Mo Willems. Published by Hyperion.
I bought this at a Scholastic Book Fair, then realized the author is the same one who writes all the Pigeon books. Luckily, Kohls was selling stuffed Pigeons, Ducklings, Piggies and Elephants this summer so I got them all.
I teach the song, then we read the book and sing the song before we turn the page.