As Imagination Soup notes, this picture book is a great choice for preschoolers, since it as clear, repeating text and a story that emergent readers can relate to.
"Based on the song of the same title," Imagination Soup says, "sing about the creatures who go to Katy's birthday party--and what they wear. Mary where her red dress. Henry wore his green sneakers. Katy wore her yellow sweater. The color and clothing repeat. (Green sneakers, green sneakers, green sneakers.)