This is a reading, rather than writing, question.
My 6 1/2 year old is completely obsessed with Harry Potter. I was comfortable reading the first two books to him, and reluctantly agreed to the third. He's nagged me so much about the fourth that I demonstrated horrible parenting (giving in to nagging) and started reading an edited version to him (cutting out the parts I think are too mature/disturbing), but as I predicted he's having a bit of trouble following the more complicated plot and more sophisticated writing style.
So I'm looking for suggestions of books that will satisfy that craving he has to get completely immersed in a book without being too mature for him. They don't have to be about wizards, but need to have that certain something that makes kids just go crazy.
We still read picture books sometimes and he's been happy enough with my recent picks of Charlotte's Web and Mr. Popper's Penguins, but they don't excite him like Harry Potter does. The last set of books he got very excited about were K. V. Johansen's Torrie books (if you haven't read these MG fantasy books, I highly recommend them).
If I don't come up with another book/series to suck him in, he's going to start bringing Magic Tree House books home for me to read to him again! (Mary Pope Osbourne has my profound respect for the reading empire she has created that has inspired so many kids to love books, but I just can't bear to read any more aloud, and he's several months away from being able to read them on his own.)