Terrible Things: An Allegory of the Holocaust

I think that part of the problems involved in trying to evaluate whether or not this is an appropriate book for children is that, as adults, we are coming at the material understanding what it is an allegory for. It makes us shudder to think of it because it is so well-written and conceived. We cannot see it without the connections it makes.
Looking at it with this admitted lack of perspective i think that it could be appropriate for children because the animals are "taken away", there is no mention as to what happens to them (and, historically, many people were unaware/in denial of what was happening while the Holocaust was happening.) Discussion with the children doesn't have to include what happened to the animals (and i realize that the unknown is almost more frightening, but it is hard to know how children will actually react as they don't have our pre-conceptions.)
It is definitely appropriate for older students as a discussion point about the Holocaust.
The ideas presented (not the literal, historical record, but their allegory) are important to talk about from an early age and i believe the author put much thought into how to do so and was successful. Parents and teachers should put as much thought about how (or if) to share it with their children.