My wife and I had a fight (she was yelling, no physical fight) in front of our eight-month-old son a while back, and hearing him cry made me feel really bad. I guess at his age, he won't remember shit, and I'm sure most parents have loud arguments at some point, but it's scary to think of how arguing with your spouse can fuck up your kid.
As someone that has parent fighting all the time, you don't remember what exactly happened but the feelings of confusion, fear and sadness are always in the memory and stay with you.
Yeah, things that happen before you start developing long term memories can still cause life-long damage. In some ways it can be worse, since you can't recall it clearly enough to discuss or work through the issue in therapy. If you can remember it, you can talk about it and try to develop strategies to cope with the trauma.Unfortunately, I remember shit like that when I was 3 years old forward, plus all the sentiments you've said above.
Source: I used to be a grief/loss counsellor, specialising in working with kids/families. Also a DV survivor.