Question for Christians about Animals?

I've heard it said that Christians don't believe that animals have souls like humans do, and for that reason animals do not go to heaven. However the thing that seperates us from animals is that Adam and Eve ate from the tree of knowledge and gained an understanding of death. Doesn't that mean that animals are pure souls as God intended them to be and it is we humans that are imperfect? Why then do animals not go to heaven?