DS quite enjoyed all ~13 Oz books at that age. Books of Wonder has nice reproductions of the originals that have large type and light illustrations. Some of them are OOP but still easily available at most libraries.

In a similar vein, Michael Hague did nice illustrated versions of both volumes of Carl Sandburg's "Rootabaga Tales".

More on the adventure side... DS also enjoyed all of Ransome's "Swallows and Amazons" books. We did them as read alouds and he has read all of them himself once or twice and will probably read all of them again this summer.