The Wheels on the Bus by Paul O. Zelinsky

From chapters.ca:
When The Wheels on the Bus, by Caldecott Medalist Paul O. Zelinsky, broke onto the scene twelve years ago, it created a sensation with its clever characters, sly subplots, luscious colours, and the incomparable flair of its moving parts. Almost a million young readers have enjoyed the wheels that go round, doors that open and shut, and people who go bumpety- bump. Today it remains as fresh and engaging as when it was first published.