After a few years dealing with children's books a dealer can usually date a book (at least by decade) by illustrator art alone. Here are a few examples of 1940's and 50's dj cover art from books in my inventory.
Trudy Terrill Eighth Grader by Bernice Bryant. Dj by Alice Carsey. Published by Bobbs-Merrill, 1946.
Old Charlie by Clyde Robert Bulla. Illustrated by Paul Galdone. Published by Crowell, 1957.
That Jud! by Elspeth Bragdon, illustrated by Georges Schrieber. Published by Viking, 1957.