I feared my closet when I was in the single digits, still do kinda. It is the always-open kind and resembled a big-toothed, moustached face from a childrens horror book that was read to my class in school near halloween. I cant read 'Stories to tell in the dark' because the illustrations make me shiver like wild.
I don't remember many fears besides fear of the darkness and murderers and Mr. Hyde (inspired by a Bugs Bunny cartoon even). I fear silence, I think. I have a fan run in my room at night to cover many creaking sounds. I dont have any lights in my room, but I fear the small ones on my fan and the computers. They look like malevolent eyes at night so I turn them all the way down.
My imagination has died down a lot since I was my little wild (I'm sure I had/have ADD of some kind) self. My parents were very supportive of me (Especially my INFJ father), which helped me grow out of it well.
Letting the little one know you will be there for them and talking with them about what it was that scared them and the hows and whys of the situation is, what I think, the best plan is. All humans work better if they know someone who understands and supports them.
Oh, I think having highly positive pentecostal services every Sunday helped me a lot. The spirit one feels is like a deep-tissue massage of the soul. I knew I had the Biggest Daddy Ever to keep me safe from ghosts and demons and evil things. What do I have to fear if God's my bodyguard?