When I was young my brother and I weren't allowed to cry - we'd get the 'I'll give you something to cry about' line from our father - because in his mind crying was a sign of weakness and his children weren't weak.
Has that effected me? FUCK YES! I'm emotionally retarded when it comes to moments one 'should cry' and times when you're left thinking. WTF am I crying for. However due to this 'rule' that was set down upon us. I'm the polar opposite of him, I'm a supportive person when people around me cry. I go into 'support' mode, telling them it's alright to cry, and things will be alright (That whole reassurance thing! *See previous post*) This also includes my nephews when they cry.
Children cry for various reasons, they are hurt, they feel hard done by, they are tired and need a serious nap. But being supportive is what I personally believe is important. When I ask 'four' what's wrong and why is he crying. He will give me an answer. It might be that his little brother is hogging the toy and won't share, that he feels sick, or is afraid of the dark. But it's these answers that hold the key to the emotional state of the child / person at that very moment.
If your kid is afraid of the dark, give them a nightlight simple. Why traumatize the child by forcing them to sleep in a darken room, when they are clearly visibly upset from the situation. I think I hit the nail on the head with my brother when I was with him last re his kids crying. I just simply uttered the words.... Don't be like our father!
The boys now have a night light :)
That's all I've got.