I remember a book called "The Seven Songs of Merlin" by T.A. Barron at least 7-8 years ago. It is the second of the five "Lost Years of Merlin" series. I have not read the other ones, just the Seven Songs book, but that gave me a lasting impressing that I don't think I can ever forget.
Another series would be Orson Scott Cards Ender series. Starting with "Ender's Game", then "Ender's Shadow", and ending with "Shadow of the Hegemon". Not sure if the last 2 books would be too much for a seven year old, the later two probaly has too much politics/ military/ philosophical content, but "Ender's Game" is definitely easy enough to understand.