That rating is really 3.5.
This is a very good story that could have done with a major re-write and a better editor. But, considering that it is also a first book and that the author died (aged just 33, way too young)while working on the book, those faults are easy to forgive.
I also think that editing points that I picked up on would probably not bother the targetted age group (9 -11)at all. They would just get lost in the adventures of three kids trying to safe a magical wood and the four seasons.