Mrs. Piggle-Wiggle - highly recommend
Beverly Cleary
Charlie and the Chocolate Factory
Pippi Longstocking
Princess Tales by Gail Carson Levine
Flat Stanley
Boxcar Children
Encyclopedia Brown
Just-So Stories
Boxcar Children
Ben and Me
McBroom by Sid Fleischman
All of a Kind Family
Frindle
Bunnicula
E.D. Baker
The Secret Garden
The Wolves of Willoughby Chase (might be a little scary, but I don’t think it’s as scary as Harry Potter).
The Quiltmaker picture books by Jeff Brumbeau (not chapter books, but significantly more text than an average picture book).
Where the Sidewalk Ends (quirky poetry)