Why do you think the author had Scotty hit by a car on his birthday?
Because Scotty is hit by a car on his birthday, his parents completely forget about the cake that they have ordered from a bakery. This omission leads to a series of events on which the plot of Carver's story pivots. After three days, the baker who possesses no knowledge of the child's accident and subsequent death, phones the parents, Ann and Howard Weiss. At first, Ann thinks it is the driver who hit Scotty who is calling, but then she realizes that it is the baker. Nevertheless, in her highly emotional state, she rages at the baker on the phone:
"My son's dead," she said with a cold, even finality. "He was hit by a car Monday morning. We've been waiting with him until he died. But, of course, you couldn't be expected to know that, could you? Bakers can't know everything-can they, Mr. Baker? But he's dead...."
The Weisses decide to drive to the bakery and confront the owner. But, by the time they arrive, the shop is closed, although they can hear a radio when they go around to the back. They knock and the baker curtly asks, "What do you want?....Are you drunk or something?" Still angered, Ann forces her way inside and tells her husband, "This is the man who's been calling us." Seeing her hostility, the baker tells Ann she may have the cake for half-price; then, when Ann is still seething, he amends his words, telling her she may have it for free. He apologizes to Mr. and Mrs. Weiss:
"I'm just a baker....Maybe once, maybe years ago, I was a different kind of human being. I've forgotten...But I'm deeply sorry...for your son, and sorry for my part in this."
He asks them to sit down at a table with him. Then, he tells Ann and Howard that he has no children of his own, and he explains that after so many years of baking cakes for others when he has no one himself, he has been rendered an odd man who does not know how to act. He adds,
You probably need to eat something,...I hope you'll eat some of my hot rolls. You have to eat and keep going. Eating is a small, good thing in a time like this.
From his oven, the baker pulls out some freshly-baked cinnamon rolls, and they eat together. As they share this food, the baker tells Ann and Howard of his own loneliness. In a while, the baker brings out bread that they share along with their lonely conditions; the Weisses talk with this solitary baker until the morning and find some meaning in this time shared together.
Therefore, it becomes apparent that Raymond Carver uses the birthday of Scotty as a focal point for the meeting of the parents and the lonesome baker.