Both my kids are afraid of the dark, at 6 and 8yo. I leave the toilet light on, which lights the hall outside their rooms. Even so, my 8yo wont get out of bed at all if it is night and everyone is in bed. She takes a drink with her to bed so she doesn't have to get up. They probably started being afraid at aroud 3yo. I think it is a normal thing for kids (and some grown-ups ). Both know their fears are probably irrational and there is nothing actually there to make them afraid, but it doesn't change anything!