Halloween.
And I wasn’t so much a kid when my wife and I saw it - I was 29. When we left the movie theater and went out into the parking lot to our car, I checked out the back seat just to make sure.
As a kid, probably the most intense horror movie was The Haunting, a 1963 movie based on The Haunting of Hill House.
That late 50s Earth vs. the Spider was memorable. I want to think I had some nightmares after that one.