Innocence is a trait that both the pilot and the little prince value. For the pilot, the little prince's innocence makes it important to protect and comfort him. For the little prince, his rose's naïveté similarly makes it important for him to return to his planet to protect her. Innocence itself serves as protection as well—when the little prince encounters the snake, the snake refrains from poisoning the boy because of his innocence.
Grownups are those who have lost their innocence—and as a result, have stopped seeking the truth. They care more about sums and titles than about the traits contained beneath the surface. The state of innocence is therefore valuable because it comes with perceptiveness and an ability to see the important things in life.