Hmmm, has the nine-year-old read stuff like Treasure Island, The Wind in the Willows, The Jungle Book? What about Caddie Woodlawn, Anne of Green Gables, Little Women, Strawberry Girl, The Saturdays, From the Mixed-Up Files of Mrs. Basil E. Frankweiler? The Moffatts? Roller Skates? (Most of these books are about girls.)
Have you considerd the mystery genre? What, for instance, about Sherlock Holmes novels and stories?
Also, Agatha Christie books–And Then There Were None, The Murder of Roger Ackroyd, and Murder on the Orient Express are justifiably acclaimed. Christie isn’t a Great Writer, but her plots are excellent, her language fairly simple, and her books classic “Cozy Mysteries” that don’t contain sex and gore.
Father Brown mysteries are good. Actually, anything by Chesterton is good.
The schools probably will feed your kids The Power and the Glory at some point, but Our Man In Havana is delightful, and really Graham Greene in general is most enjoyable.
The older kids might enjoy Dorothy Sayers’ novels. She’s a better writer, if not as ingenious a plot constructor, as Christie.
Your family’s sense of humor may vary, but even as a kid I always loved P.G. Wodehouse (Jeeves, Emsworth, Mulliner, Golf, Psmith series are wonderful).