Discuss the Tone and Theme of "A Small, Good Thing"

In Carver's story, "A Small, Good Thing," the tone appears to be that of sadness. The story contains a few tones including bitterness, pity, and even love. Despite this, sadness seems to be the overpowering tone. The following are the two situations that bring the sadness throughout the story:
"There was a Negro boy in surgery last night," Ann said. [. . .] "He passed away," said the nurse at the counter. (Carver)
Scotty, honey, it's Mommy and Daddy," she said. "Scotty?" The boy looked at them, but without any sign of recognition. …