To an extent, they understand that little mortals should not be given alcohol. However, the definition of what makes a little mortal little and what they're allowed to do while little has changed vastly over the centuries; where beer was once the only drinkable beverage out there and you'd give it to your babies, now it's a faux pas for anyone under 21? That's so old for them, isn't it? It's like a quarter of their whole lives! Silly!

Their own take is that anyone who is old enough to get taken to their realm is probably old enough to drink back home, too. So, if an underage character acts like they know what they're talking about, none of the fae would be any the wiser that they're not "supposed" to be drinking, but if the character points out that they're too young, the tavernkeeper will remember that, oh right, they have rules about this sort of thing don't they?