Neither of my parents were alcoholics.
That said, my father did used to keep a six pack of beer on the lower shelf of the fridge, hidden in the back, wedged behind the vegetable drawer. He'd bring it out when he would have a friend from work visit, if they wanted to have a drink, and they'd each have one.
He stopped keeping beer in the house once he decided I was old enough to know what it was, but I already knew it was there, and I remember this very clearly to this very day, right down to the Yuengling eagle logo, and the shape and color of the bottle.
Alcohol never negatively impacted my childhood, so it's not even a trauma memory. This is just a childhood memory, filed away next to the stories my father used to make up at bedtime with all of us camping out on the thick green carpet that was my bedroom floor, and the memories of watching my father stack the deck when playing Christmas Candylane so that my sister would win (because she'd throw a full temper tantrum if she lots).
If I remember my father's mild drinking habit from when I was younger, imagine what someone living with an active alcoholic can register.
Granted, I didn't know all the side effects from beer, I didn't know what alcohol was, I didn't know how bad it tasted, I didn't know a lot of things - but I knew it was called beer, and it was only for Daddy and his friends.
As a child, I understood the basic differences between beer (adult drink, I could never have any, for any reason), root beer/birch beer (my favorite soda, only one big glass or two little ones, and only on special occasions), and milk (can drink as much as I want as long as there's enough left for breakfast tomorrow morning).
Kids are frequently underestimated. I was a lot smarter than I looked, and I remember things that my parents claim I was too young to remember.
And while neither of my parents were alcoholics, my family was absolutely dysfunctional, and I remember way too much of that. About half my memories of my mother are trauma memories, which are much sharper and have much more of an impact on my life. That said, I can understand how maybe not knowing of the alcohol consumption doesn't mean they don't know something is wrong.