I received all of these books on my Kindle for free sometime last year. I finally got around to reading the first one. This is a typical mythical, magical themed book. But I enjoyed the angle it took using an apprentice to a Spook - someone whose job it is to keep the county safe from these magical creatures.
Much of the book was predictable, but I enjoyed the set-up that was happening that makes me want to read the rest. How will things work out with Alice? I'm pretty sure Tom's "mam" is a witch, but will it ever occur to Tom? Will we ever find out what happened on Hangman's Hill? And will we find out more about the current Spook's past? There are 7 more books in the series plus 2 extras. But they are quick reads. I have no idea how many pages since I read it on my Kindle.
As for letting kids read it: I think if you have a mature 4th or 5th grader, maybe even a 3rd grader, would appreciate the book. The book alludes to babies and other people dying although you don't read any graphic detail about it. But it's certainly more tame than Harry Potter.