On the subject of great kids' books, another guaranteed winner (but possibly hard to find) is the Enid Blyton's Adventure series.. Eight books, I think, of the same bunch of kids being raised by a single mom and a mysterious "secret agent" some-time companion..and getting into all sorts of adventures and misadventures.
Appropriate to read to 6-8 year olds, and for them to read themselves after that!
The Adventure Series - Wikipedia, the free encyclopedia