It might be the sense of isolation the kids feel. When the babysitter cuts off their communication with their parents, it creates a really scary and helpless situation for the kids. They are alone with someone who is starting to act very strangely, and they have no way to get help.
The sudden appearance of something strange. In the story of the face at the window, the babysitter is just going about her job, and then suddenly there's this creepy face. There's no warning, and it's something that seems out of place and threatening, which is really terrifying.
The sudden and unexplained noises are really scary. For example, in many stories, there are strange creaking sounds or thuds that make the babysitter jump. It creates a sense of unease right away.
The scariest part could be when Claire first hears the unexplained noises. It's always terrifying to be in a house and hear strange sounds with no obvious source.
Well, the contrast between the expected role of a babysitter (someone who is supposed to be caring and safe) and the appearance and behavior of a clown can be extremely scary. A clown is often associated with the circus, a place of entertainment, but when it's in a babysitting role, it's out of place. And if the clown - babysitter has some sort of 'evil' or 'creepy' backstory that is hinted at during the story, that can be really terrifying. For example, if there are rumors that the clown has been involved in strange disappearances in the past while babysitting, that would make the whole situation much scarier.
One of the scariest aspects is the sense of malevolence it gives off. It's not just about the physical things it does like moving or causing noises. It's that feeling that there's an evil entity inside the doll, constantly watching and plotting something bad. Also, the unexplained scratches and marks that seem to be left by the doll are really spooky. It makes you wonder what kind of force could be behind such actions.
The sudden transformation of the cute and innocent - looking Barbie into something terrifying is very scary. For example, when its eyes change color or it starts to move in an unnatural way.
In a scary dora story, the isolation and being trapped in a spooky place are really scary. For example, when Dora was locked in the haunted house and couldn't get out. She was alone with all those creepy things and didn't know what to do.
When something from Emily's past or the past of the place she's in comes back to haunt her. For example, if there's a dark history associated with the house she lives in and things start to happen that are related to that history. It makes you think that the past can't be escaped and that there are forces we don't understand at work. In the case of the old diary, it's like the past is reaching out through the pages to get to Emily. That's really terrifying.
The feeling of being trapped is also very scary. In a harry scary story, if Harry is in a spooky place like a locked cellar and there seems to be no way out while something menacing is approaching, it's a truly frightening situation. He has no escape and is at the mercy of whatever is there in the darkness.
As I don't know the story, I can't say what the scariest parts are.