The archetypal setting in A Child Called "It" was mainly a "cave" which in the book was the basement. When he is sent down there he dwells on his life, how to out smart his mom, and how to get food. If you wanted to really use your imagination you could say the rest of the house is the sea, because it is chaotic around his mom. David as an archetypal character may be best described between an innocent embarking on a journey (trying to figure out how best to survive and change his life) or an orphan, because he is unwanted and more like a slave. Then the mother would be more like a wicked stepmother or you could even go as far as to say David's mother is like a king, because she expects immediate obedience. Finally the archetypal actions/events in the book would be all three. First it was a journey, because he is an innocent embarking on a journey to get away from his life as a "slave". It is also a Rites of Initiation due to the reason that he deals with the parent fights often and goes through a lot of trauma after being unwanted and abused by his family. Although it is Sacrificail Rites too, because his journey fails, and he does things he is not supposed to.
http://www.bookrags.com/A_Child_Called_"It"
This link will be helpful if you haven't read the book and can't understand my writing, or are interested in the novella. It gives you the summary, theme, styles, quotes, etc. This website is very interesting and helpful.