Young children go through phases with their reading, most of them driven by the basic human need for security. In early childhood they want the same bedtime story read to them over and over again, and parents go mildly insane doing 100 reps of Goodnight Moon or, in my case, The Cow Who Fell in the Canal. Then when they first begin to read, it's repetition of simple sounds and words, like Sam-I-Am in Green Eggs and Ham. The jump to chapter books is an important one, and it's not a coincidence that there are many books in simple chapter books series like The Boxcar Children. My children started reading the Boxcar Children when they were anywhere from 4 to 7 years old, and two of the four have read every available book in the series ... but no child I've known has ever continued reading the Boxcar Children past age 9 or 10. The repetitious format of formula fiction is self-limiting, and kids must move on. Many times, they move on to something like the Guardians of Ga'Hoole, a series of chapter books about heroic owls by Kathryn Lasky. With many books to bring back familiar characters, this series offers more literary merit and more complex storylines. But still, the reading level is most appropriate for ages 7 to 12, with few over that age who are more than tolerant of the overall story.
I admit, I was dubious about Lasky's Ga'Hoole books after reading her Memoirs of a Bookbat, a Judy-Blume-ish adolescent memoir about the evils of censorship riddled with badly-disguised bigotry against evangelical Christians. But my firstborn son had fond memories of the Ga'Hoole series: he said it kindled a love of heroic fantasy literature in him and he compared it favorably to Brian Jacques' Redwall books, which we all love. There is a film version of the first three books, with gorgeous animation and visual effects, which our family watched on TV, although I dozed off at a few key plot points (probably no fault of the movie, I was just very tired). So I gave the series a try, checking out audiobooks of the first three books from the library, and listening to them in the car with the family. They had great production values, and the writing is very good. Lasky has written close to 100 books, and she knows all there is to know about plot and pacing and character development. But I can't say I love these books. Maybe it's the juvenile gross-out humor and TMI about every minute detail in owl life. Maybe it's the improbability of believing in a post-apocalyptic world where owls have evolved to take the place of humans, including mastering metalworking and warfare. But I think most probably it's the idea that some owls evolved an abnormal psychology that necessitates domination of other owls through brainwashing and concentration camp tactics. It's most likely an attempt on the author's part to portray World War II in a less threatening way so kids can process it. But if you're looking for an animal fantasy/adventure story for elementary readers, I believe there are better options.
Some children's books you just can't wait to read to your kids; some, if you have eager readers who outstrip your ability to stay ahead of them, you just hope will not damage your kids if you never get around to reading them first. The Ga'Hoole books do observe this primum non nocere principle, mostly. The action is engaging and, if you don't overanalyze things like I do, there's always something exciting happening. There are several charming characters: Soren the barn owl, Gylfie the elf owl, Mrs. Plithiver the blind nestmaid snake. So, these books are great fodder for the eager readers, as long as they are not disturbed by potentially dark themes (fratricidal owls who join a conspiracy against owl-kind, ghosts, forced labor and re-education camps under a strange totalitarian system). As a child, I would have more likely been confused by some of the moral ambiguity in the minor characters, and bored by the technical details about owls' digestive systems. As an adult I was ready for the third book to be done, and when one of the CDs was unusable, took that as a sign to quit listening and check out something by another author.