My 4-year-old doesn't sit still so I haven't read her chapter books but I might start with that this summer. I'm not sure just how it will go.
But some favorites here are:
Wind In the Willows
The Phantom Tollbooth
The Mouse and the Motorcycle books
Or really anything by Beverly Cleary. In fact, my girls have a similar age spread as Beezus and Ramona. I might start with one of those books.
Add your favorites!