This is book number 18 in the Redwall series.
I started reading this series when I was 8, I am now 30 and I still re-read it and get new things out of it. Does your kid looove the Warriors series? Their mind will be blown by the world of Redwall. Imagine, if you will, an egalitarian community of woodland creatures who fight tyranny, go on epic quests, and throw the best parties with the most scrumptious and elaborate meals you've ever read about.
Every creature, big or small, shy or outgoing, female or male, is valued and has an important role to play. Sometimes it's a formerly enslaved squirrel, or maybe a mute badger grandmother, or perhaps a young ottermaid who has perfect aim with a slingstone...— From Anje