We've found lots of picture books between a 3rd and 4th grade level that aren't too long. smile Scholastic's book wizard can help you find them.

A few that I can remember DD really enjoying (in no particular order):

The Three Little Dinosaurs, by Jim Harris
Bill & Pete (and other books), by Tomie DePaola
Outside Over There (and other books), by Maurice Sendak
Parts (and other books), by Tedd Arnold
Super-Completely and Totally the Messiest, by Judith Viorst
The Seven Silly Eaters, by Mary Ann Hoberman