Scream is not based on a true story. It's a product of the imagination of the filmmakers, designed to scare and engage the audience with a made-up plot.
A kid might scream at a scary story because they are not used to dealing with fear in that way. Their little hearts can't handle the sudden rush of adrenaline that comes from hearing something really scary. It could also be that they have no experience with such intense emotions, and the only way they know how to respond to the fear the story creates is by screaming.
Maybe ckid is easily frightened. Scary stories often have elements like sudden scares, spooky characters, or eerie settings that can make a person scream.