The theme of this story revolves around class distinctions and discrimination. Society is obsessed with appearance, and this plays into class separations. The rich are respected not because the are "better" people, but because the appear "better" - nicer clothes, fancier housing, etc. This focus on appearance is symbolized in the doll's house the girls receive. It is a perfect imitation of a rich home, and earns the girls the respect of their classmates, as if they actually did own a rich home.
However, this appearance of respectability is often false. Two girls are consistently withheld from visiting the doll house. The Kelvey girls come from a poor household. Add to this that their father is in prison. The appearance is that they are "less" than everyone else, and so they are prevented from visiting the doll house. However, Kezia realizes how unfair this is, and tries to obtain permission for the Kelvey's to come to the house. Unfortunately, her "respected" family refuses to allow such "dangerous" little girls to come to the home. The discrimination first shown by the older Burnells and then by the classmates of the Kelveys demonstrates the unfairness in social class structure.