Most of these are seconds of other things, but I remember at that age I read (and some still reread):
The Little House books
The Secret Garden and The Little Princess by Frances Hodgson Burnett
pretty much anything by Beverly Cleary (particularly the Ralph S. Mouse books)
The Narnia books
Harriet the Spy by Louise Fitzhugh
Encylopedia Brown books by Donald Sobol
The Wizard of Oz books
The Doctor Doolittle books
Heidi
And pretty much any book about animals
