OK, I'm just going to expand my pick without editing - now that I have a bit of time!
HARRY POTTER
1. Harry Potter and the Philosopher's Stone
2. Harry Potter and the Chamber of Secrets
3. Harry Potter and the Prisoner of Azkaban
4. Harry Potter and the Goblet of Fire
5. Harry Potter and the Order of the Phoenix
6. Harry Potter and the Half-Blood Prince
7. Harry Potter and the Deathly Hallows
I began reading the Harry Potter series of books in the space between the 3rd and 4th in the series. I read through the first three in a series of about two weeks when I probably should have been in class up at the University of Alberta. I've found them well-written, well-paced, exciting books right from the beginning.
One thing I love about them is the characterization - people change throughout the series, don't remain too static and are complex without being too complicated. After all, these books have been marketed towards children. Interestingly enough, however, J.K. Rowling has stated that she had no particular age group in mind while writing the books.
Another great thing about this series is how planned out it is. Things that are set up in the second book pay off later in the series; the consistency within the universe J.K. Rowling set up is excellent as well.
Finally, I find this point best suits why I think these are great books for children: the tone and mood of the stories grows and changes with the characters (and the readers) as they age.