I'm thinking of reading a ghost story to the frightened children before bedtime
Don't you think that that is just going to scare them even more?
No, they love ghost stories!
If the child is already scared, it is a good idea to not tell them a scary story. It could keep them up and ruin their mood. Maybe you can read another story.
I'm going to say no at first, then I'll slowly start to freak them out with the ghost story.
This is not a good idea. This will only serve to frighten the child more. Maybe a regular bedtime story would work better.