Picnic, written and illustrated by Emily Arnold McCully, is one of my daughter's favorite books. This is one she'll get out on her own to look at over and over.
There's not a lot of text in this story. Most of it is told through pictures. It's the story of a small mouse who gets separated from his family while going on a picnic. The lost mouse is sad and lonely, and the family searches for him until they find him. Eventually they do and everyone is happy again.
The pictures are charming in this story. There's large flowers everywhere, and lots of little mice playing different games. It's a great example of how important every member of the family is, down to the very smallest.