I don't know about the trauma, but even though I wasn't allowed to watch the evening movie, later I was always drawn to Sci fy horror films when I was a teenager and even now. So when I got custody of my two daughters, I didn't have that old-fashioned way of looking at things.
I had seen this film for the first time when I was a teenager, and I was always waiting for the continuation of the saga, and one day the first one was shown on TV one weekend. I hadn't watched the TV program, and was getting ready to spend a TV/pizza evening with my two kids, because it was a sort of rite for the Weekend.
I'll skip over the details but they ended up convincing me to watch Alien, the first part. They were only 8 and 11 years old at the time. I remember the first time when I went to see it in the cinema, I almost shit myself. In short, they spent the entire film clinging to me, screaming like bats, but the next day, they absolutely wanted to see the rest of the saga.
Rest assured, they are in very good mental health now. No trauma to report, and they're looking at much worse things today.
The most shocked of all are the adults most of the time.