The poor and dispossessed brothers represent mankind's thirst for freedom, for opposition and resistance. They symbolically kill Darwin, the story's central power figure and the main avatar of the hegemonic singularity. Yet they do so in an attempt to erase the boundaries between themselves and that oppressive structure. Darwin, whose domination of humanity has rendered him godlike, grants them their wish and transforms them into the insipid tourist children they wish to become. In the end, their struggle for justice and self-determination has come to nothing, and they go, indistinguishable from the other siblings, for ice cream.

You should also consider its similarity to the 1975 short story 'Let's go to Golgotha'