They're scared of everything in their room at night
Night fears in children between three and eight are real, developmentally normal, and not evidence of anything wrong. The fear lives in the imagination, which has just become powerful enough to generate things that feel present. The most common things that accidentally keep it going are rituals that confirm the threat and reassurance that sounds uncertain. What helps most is calm certainty, low light, a door open enough to hear ordinary life continuing, and a story that gives the dark different company.