Aw, my ds was such a sweet tender heart at that age too! Here are a few series we enjoyed after the ones you listed:

A few sweet series to try: Humphrey books! He is a class hamster. Geronimo Stilton, head of a mouse newspaper/adventure books
Mysteries: Cam Jansen, Bones, The Mysterious Benedict Society (we LOVE those!), Nancy Drew/Hardy Boys, the 39 series, A to Z Mysteries, Magic Tree House
General: The Chocolate Touch, Chocolate Fever, Lemonade War series
Classics: Narnia, Matilda, Shiloh, Old Yeller, The Yearling, Where the Red Fern Grows, Pippi Longstocking, Sounder, White Fang, Hatchet, etc.

Enjoy! smile