"A Perfect Day for Bananafish" contrasts the world of children (imaginative, curious, pure, and innocent) with the world of adults (materialistic, selfish, shallow). As you can see, the story glorifies children and to some degree condemns the attitude of most adults. It even explores the idea that children are somehow more spiritually advanced than adults, more capable of seeing with the soul rather than the eyes.
Seymour is better suited to the world of children than to the world of adults.