Why does horror have to be for adults? Can’t there be a kids horror movie?
These are some kids horror movies I found on IMDB's horror list:
Casper: A Spirited Beginning (1997)
Casper's Haunted Christmas (2000)
Scooby-Doo & Batman: The Brave and the Bold (2018)
The Little Vampire 3D (2017)
Daffy Duck's Quackbusters (1988)
Bugs Bunny's Creature Features (1992)
Bugs Bunny's Howl-oween Special (1977)
Tiny Toons' Night Ghoulery (1995)
The Adventures of Ichabod and Mr. Toad (1949)
Mickey's House of Villains (2001)
The Batman vs. Dracula (2005 Video)
Alvin and the Chipmunks Meet the Wolfman (2000)
Alvin and the Chipmunks Meet Frankenstein (1999)
Scooby-Doo and the Reluctant Werewolf (1988)
Scooby-Doo! Frankencreepy (2014)
Lego Scooby-Doo!: Haunted Hollywood (2016)
The Black Cauldron (1985) - Disney
The Monster Squad (1987)
The Haunted Mansion (2003)
Scooby-Doo 2: Monsters Unleashed (2004)
Frankenweenie (2012)
The Pagemaster (1994)
Return to Oz (1985) - (Disney)
There are also a bunch of short films that are on IMDB's horror list, but I don't know if shorts are eligible for the countdown:
The Case of the Stuttering Pig (1937) - Porky Pig Short
Jeepers Creepers (1939) - Porky Pig Short
The Great Piggy Bank Robbery (1946) - Porky Pig Short
Hair-Raising Hare (1946) - Bugs Bunny Short
Dr. Jerkyl's Hide (1954) - Sylvester the Cat Short
Claws for Alarm (1954) - Porky Pig and Sylvester Short
The Duxorcist (1987) - Daffy Duck Short
The Night of the Living Duck (1988) - Daffy Duck Short
The Legend of Sleepy Hollow (1949) - Bing Crosby Short
The Skeleton Dance (1929) - Disney Short
The Haunted House (1929) - Mickey Mouse Short
The Mad Doctor (1933) - Mickey Mouse Short
Betty Boop's Hallowe'en Party (1933) - Betty Boop Short
When Harry Met Sally 2 (with Billy Crystal and Helen Mirren - 2011)