Goodnight, My Duckling, by Nancy Tafuri, Scholastic Press, 2005. Baby to Toddler to Preschool.
Once of the first books I bought for my son, before he was even born, was Nancy Tafuri's I Love You, Little One. I started reading it to him when he was only a few weeks old, and now that he is almost four-and-a-half, we still read it. I picked up I Love You, Little One because of the wonderful cover art. I picked up Goodnight, my Duckling for the same reason.
The text in Goodnight, My Duckling is simple enough for my son to read on his own, and it is charming enough that he wants to read it. Those two qualities made this book perfect for young beginning readers.
Nancy Tafuri's illustrative style is a wonder. She renders her artwork so accurately that it is even very young children have no trouble recognizing the animal (or plant or object) she has drawn, but in a way that is infused with such sweetness and loveliness.