Children may learn from the sober parent and become perfect little codependents who completely wipe out their own wishes and desires and sees it as their role in life to make sure everyone else is happy. I have one of those.
Children may learn from the drinking parent and become bullies who use their anger and put-downs to get what they want, and to put their wishes and desires ahead of everyone and anyone else's, regardless of how miserable it makes the people they love. I have one of those.
Mine are not yet of dating or substance-abusing age, so I don't yet know what choices they will make there, based on their early life experience. They've been diagnosed with PTSD. They're in therapy. It will be with them their entire lives. That, I know.
As for when they start noticing? An infant notices being screamed at or lifted roughly or ignored. And after that it only gets worse.