Well, they're kind of right, and I'm not too worried about it.
It is too short, makes no sense (in terms of its conclusion), and is aimed at the sixth grade.
I would assume the middle comment is from someone aged around twelve, while the others are from older readers - the problem with putting a book into the children's and young adult categories. The older readers aren't impressed.
I really only posted this (the comments) because I thought it was funny.
Overall it's got a rating of three and half stars at Apple, the only place where it has any ratings, and I think that's about right, or maybe generous, if anything.
It's not badly written. It "has a good use of words". And it is interesting, as far as it goes, but I wrote it ten years ago, and I'm not overly worried about its reception. I know its flawed. I really only want to use it as a springboard for the other children's/young adult novel I have (written a little later, and actually novel length). It's probably not a good idea to use something not very good to promote something better...
Anyway, when I've finished redrafting the next, I'll probably give over writing for children. It's a long time since I've tried it, and it doesn't really interest me anymore.