D.P.
Both our girls went through being scared of things in the dark at some point.
Since we are christians we handled this in two different ways. We taught them the verse from Ps. 56:3 "When I am afraid, I will put my trust in You (God)" We would talk about all the things that God does to care for us and how we can trust in Him. We also made sure we had an adequate night light and did a thorough check of their rooms each night to reinforce that there wasn't anything there and they could trust us and God to care for them.
Hope this helps!