Well, I was raised primarily by a bipolar alcoholic. Talk about opposite end of the spectrum, right?
I would probably not react to it, but instead, engage the kids. Ask them who they are imitating? (which is better than asking "where they got that from" which often signals "trouble" or "bad"). I would take the opportunity to have a lot of good talking about alcohol. Do they know what it is? How it's different from coffee or tea? Did they know there are laws about it? Do they know why? Do they know what can happen if they drink to much alcohol vs. drinking too much tea? Things like that.
I think if they really understood those things, it might be less attractive. And these are things that may take more than one chat opportunity to cover. My husband's family is Italian and as he grew up (here in the US) wine was pretty much available--always (he also spent 9 summers over there, where it was also readily available). When my son was 2yo, dh's gma dabbed her finger in wine and rubbed it on my son's lips. I seriously didn't even know how to respond to that.
He's now 9yo. We don't drink often, but occasionally have wine. We try not to make it taboo. If they ask, we let them smell it. They have each dipped a finger in to taste. But they know that it will hurt a growing brain and they know that it will hurt an already grown brain if there's too much, and how it makes people unable to control their actions because it numbs their brain--which can mean they don't realize they shouldn't drive a car because they CAN'T drive a car and people get killed a lot that way. But unless it comes up naturally, we don't talk about it. We've had it come up naturally enough that my 9yo is pretty well-versed on what alcohol is used for in our culture and how it can be harmful. I don't think he'll never drink, but I don't think he'll be irresponsible.