I believe that foreshadowing is used in this story to build up tension and to make us feel like something really bad is going to happen. Everytime we get a look at the inside of the nursery, it feels really dangerous. It is hot and dry and the animals seem really scary. The screaming also really sets up the idea that something bad is going to happen. I think it is done very effectively.
If the story hadn't ended there, I think Mr. McClean would probably have died too. The kids don't hate him, but they probably realize he would tell on them if they let him go.