I grew up with a book called Harry the Dirty Dog, which I remember loving. It's a simple story: Harry's a beloved family dog who decides to run away before bath time. He goes out on the city, turns into a black dog with white spots after his filthy adventure, and comes home to a family that doesn't recognize him. Right before he runs away for good, he remembers where he buried the bath brush and begs to be cleaned. This is out of character for Harry and the children love the idea of throwing the new found dog into a tub of bubbles. Of course, bubbles clean the filth and the black dog with white spots returns to the white dog with black spots. "It's Harry!" It's the perfect length for Cole's short attention span and the pictures are vintage and lovely. [And for us adult readers, it mirrors the wayward Prodigal Son story in a strange, touching sort of way.]
Harry the Dirty Dog does have a board book version, a version in Espanol [Harry, el Perrito Sucio] and a couple of sequels.