One of my earliest memories of a movie creeping me out as a kid would be the 1953 original INVADERS FROM MARS. I caught it on television when I was probably no older than six or seven on what must have been a black and white set because I was recently surprised to find the movie was actually shot in color despite my recollections. So this kid sees a flying saucer land in this spooky field out behind his house in the middle of the night and tries to convince his parents and the authorities of what he saw. Problem is, each time someone investigates they get dragged down beneath this sandpit that the saucer has burrowed beneath.
What's worse is that these victims come back…different. The kid's father, who was sucked into the ground, is cold and even hostile toward his own son. At one point the father even smacks the kid down to the floor when his son spots a strange growth on the back of the dad's neck. Soon the father is taking his wife up to be abducted and reprogrammed and the poor boy doesn't even know his own parents anymore. As a child, the Martians (when we finally see them) were much less scary than the thought of my parents suddenly becoming unfamiliar or mean. To this day I still sometimes double check the back of my parents' necks for any strange protuberances!
The art direction in this movie is amazing I love the police station set and the bizarre almost OZ-like trail up to the hill where the U.F.O has planted itself, a stark contrast to the overuse of stock footage when the army comes to save the day!