How to stop kids from watching horror movies?

My kids like to watch horror movies. Whenever these kinds of movies come on screen they try somehow to watch these movies.

After watching these movies they experience negative effects like trouble falling asleep, fear of the dark, nightmares, anxiety, increased concerns about possible dangers that can befall them.

These negative effects sometimes last days or weeks.

My main concern is how I stop my kids from watching horror movies and their side effects.