Madeline L'Engle is ridiculously difficult for a child to understand. I remember reading her in my fourth grade class at age 9 and was like: "What is this lady on?" (Not verbatim, of course.) Her writing is typically darker than the exaggerated works of Dahl, so I wouldn't recommend her for a five year old.
How about Shel Silverstein? It's "poetry" but still fun to read (and listen to if you can find it on tape).
Too bad you don't know French (I'm assuming, here)- I LOVE "Le Petit Nicolas" by Goscinny Sempe. I have yet to see them in English, but the books are just hilarious and remind me so much of my childhood dreams.
Edit: I just found a copy in English. Here's the link:
http://www.amazon.com/gp/product/071...books&v=glance