I liked this ... I went primarily with the audio (I had a physical and Kindle copy as well) and I really do think the audio is the way to go.  Kim Mai Guest was the narrator, and she really brought Ess to life, I loved her little voice.  

The story was compelling ... but maybe too metaphorical even for me (so I do wonder what younger readers would think of it).  Reading the top review (by author Rick Riordan) who said "The book is, of course, a metaphorical look at childhood, and what it means to become an adult" well, it seems obvious now that it's pointed out to me, but I'll admit while I was finishing the book up, I was a little "umm, that's it? We don't get any explanation?"  Even with out, I did like it and will think back on it fondly, although I don't know that I'd go out of my way to recommend it or feel compelled to keep my copy (it was intended for the Little Free Library, but sometimes I have trouble parting with favorites). 

It was interesting to have this mystical island where these nine children survive, and thrive. Where all the plants are edible, where once can't get seriously hurt (the snakes don't bite, the wind won't allow you to fall off the cliff), going potty is "wishing" ...  where the eldest (maybe 12ish?) is in charge of the group and of the youngest "care" teaching them (around 3 or 4?) to swim, read, help with tasks. Where everyone gets along (no Lord of the Flies here). 

I do love the cover image.