Mostly everybody here says its a great series, but it has some things maybe not for 5-9yos?
I'm a 13yo consumer and I think its fair to say that this series has peril, some bloody bits, and scary creatures (at times showing their innards and gross saliva). So in short, expect fantasy violence. The protagonist is a shallow build of a character's personality, and things like this make me want to just break into the book, and tell them what the heck is going on! The drawings are very high quality, so is the writing, but some of the main people just annoy me...
Emily (the protagonist) just takes matters in to her hands a bit too much, and is just plain stubborn.
Again though, I love the book! Just a heads-up for parents.