Children shine because they are fully present - living in the moment and reacting from an honest and spontaneous core. They have not yet become self-critical and remain the centre of their universe. Children are able to immerse themselves in play and discovery without the need to control the outcome. Childhood is a time of innocence and joy.
Like a trophy that is brand new, children shine. They shine because they live their lives without inhibition. Of course, soon they will become deeply self-conscious and self-critical. Like the trophy that becomes tarnished, so too an adult life.
The author is saying that we should never lose touch with our inner child and our ability to shine.