In order to fully understand what the Little Prince symbolizes for the pilot, it's important to first understand the pilot, including his desires and needs as a character.
At the beginning of the story, before he meets the Little Prince, the pilot describes his own childhood. The pilot is an imaginative child who loves drawing. He draws a creative picture of a boa constrictor swallowing an elephant. However, the adults in the pilot's life fail to understand the drawing. The pilot tells us, "The grown-ups' response, this time, was to advise me to lay aside my drawings of boa constrictors, whether from the inside or the outside, and devote myself instead to geography, history, arithmetic, and grammar. That is why, at the age of six, I gave up what might have been a magnificent career as a painter." This event represents the beginning of the death of the pilot's childhood imagination. The pilot's imagination is slowly crushed and extinguished by adults who think of success in terms of money, ambition, and intellect rather than creativity, freedom, and love.
So, later on when the pilot meets the Little Prince, the Little Prince's natural curiosity and freedom fascinate the pilot. The Prince asks the pilot to draw him a sheep, which causes the pilot to remember his early love for drawing that he has since abandoned. Through stories of his travels and his great love for a rose, the Prince's open mind and sensitivity contrast sharply with the adult characters' hardened, narrow minds. The Prince helps the pilot regain his own childhood curiosity, wonder, and love for the world.
Thus, for the pilot, the Little Prince symbolizes the purity and open-mindedness of childhood: the ways in which children who are still unaffected by adults and adult ideas of success are capable of loving the world with unparalleled freedom.