Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Ironic, Sympathetic
We get the sense that whoever is narrating "The Rocking-Horse Winner" has it out for the adults, but remains sympathetic toward the boy. The general tone is pretty ironic—statements about Hester's beauty can never be taken at face value when everything else in the story tells us that Hester has no inner beauty, and maybe Uncle Oscar's wealth comes only from his ability to exploit others, not from luck.
This irony takes a back seat when we get to scenes with Paul. Since the narrative of the story tracks Paul's gradual deterioration, we feel bad for Paul and his tragic death. The other characters? Not so much.