Careful examination of this short story will help you find the answer you are looking for. We are told that Doodle and his brother, the narrator of this moving story, take up lying to help pass the time when they go out to walk. Because Doodle has recently learnt to walk for himself, we can assume that the lying was a distraction that helped him reached his destination without stopping and allowed him to gradually increase the distance he could walk when he went out with his brother. In the narrator's own words, Doodle was a "terrible liar", and his lies reflect his inability to distort the truth. We are told that he had a favourite lie:
His favourite lie was about a boy named Peter who had apet peacock with a ten-foot tail. Peter wore a golden robe that glittered so brightly that when he walked through the sunflowers they turned away from the sun to face him. When Peter was ready to go to sleep, the peacock spread his magnificent tail, enfolding the boy gently like a closing go-to-sleep flower, burying him in the gloriously iridescent, rustling vortex. Yes, I must admit it. Doodle could beat me lying.
Note how Doodle's inability to lie helps reflect his position as an innocent in the world, an impression that is heightened by his child-like trust in his brother and his general naivety, which is perhaps confirmed by his death - he was a character who was not meant for this world in so many ways, as is foreshadowed by the death of the Scarlet Ibis that Doodle is described as at the end of the story.