Take time before the session and find a quiet place for reflection. How do mystery and shadows intersect for you? From the point of view of a young child (and sometimes, perhaps, an adult), shadows contain or come from the unknown, which can cause of fear. A large, threatening shadow that stands your hair on end may turn out to be a pile of laundry or a bunch of bushes. Overcoming the unknown is one way to shrink the mystery and shrink the fear.
Another way to feel less afraid is to reflect on those who have overcome their fears. Who comes to mind when you think of models and mentors for overcoming fear? What did these people do to overcome their fear?
Still another way is to take a lighthearted attitude toward shadows. Being playful makes the shadow's mystery diminish—much like whistling a happy tune when you're scared.
Reflect on your own responses to fear and what you do to diminish fear. Bring that awareness to your work with the children.