Kids' minds are still developing, and horror stories can be too intense for them. It might cause excessive fear and anxiety, which could have a negative impact on their mental health. For example, they may become overly jumpy or start to fear things that they shouldn't in normal life, like the dark or being alone.
Horror stories often contain disturbing and violent elements. Kids at a young age may not be able to fully understand or process such content in a healthy way. They might misinterpret it and develop wrong ideas about the world. Also, it could desensitize them to violence at a very early stage, which is not good for their emotional and social development.