I don’t think there will be problems in this situation. But generally, keep in mind that parents cannot give consent for their children to break the law, especially if the children are adults.
@!sylvan8798 - I have never served “minors”. My definition of a minor are those under 18.
Do it or don’t do it, but ‘permission’ from the parent means nothing. If you have to ask, I think you know the answer that it isn’t okay. I’d get the sparkling cider and not mention any other options. Do you think a bunch of 18 year olds will really care that you didn’t offer ‘real’ champagne, especially just one small glass? They never expected to drink with you before, so why should they now? If they really want to drink on NYE, they’d pick a different activity like a big party with their friends or staying home with their parents (who could provide alcohol) and not a trip to your house. This is 5 minutes of a long weekend. They’ve picked to spend it with you, OP, and they get the activities you plan. I don’t think any of them will care that they didn’t have champagne. If they were 1-2 years younger (17) you wouldn’t serve it. They are not 21, they get no alcohol from you. Easy. No calling parents, no issue with one parent saying yes and another no, no breaking the law, no guilt on you.
As someone else said, you wouldn’t offer weed, and that’s legal in many states for 21 year olds. Why do you NEED to offer alcohol? (ans: you don’t)
Military members can legally drink on base at 18, so the government does recognize that this group gets more privileges than other 18 year olds.
Full disclosure - I grew up drinking all the time with alcohol provided by my parents, other parents, and most often 18 year old friends who were giving it to us illegally. Didn’t make it right. I didn’t care if some parents gave us wine at dinners or picnics and others would. The difference here is that OP asked the question, so must have some concerns. Don’t feel comfortable doing it? Don’t do it.
Maybe kids on CC are different, but most young adults in college I know do expect to have some alcohol on NYE. I would rather serve those visiting young adults few glasses of wine/champagne at home than have them go out to a party. My gut tells me some of those guests may ask OP’s kid what else is going on in town on NYE. My .02.
exactly, oldfort. I think a family NYE celebration is lovely, and yes, I would expect champagne/wine to be part of that for anyone in college or older. Far preferable to the alternatives. I recognize the host is under no obligation to provide alcohol at any time for anyone of any age-I have attended middle-aged NYE celebrations, where, to my surprise, no alcohol is served. But I was a little disappointed, and I would expect my kids would be as well. It is a custom and tradition to toast in the New Year, and this gathering sounds perfect. What would have been done years ago is not relevant; they weren’t in college years ago, and frankly, if they are in college, they have all had drinks before. So do as you wish, OP-I would be glad you were opening your home for such a gathering and inviting them to stay over.
@twoinanddone You cannot drink on base at 18, it is 21 in the United States. Out of the states it is more flexible and can be 18 but he found that they still didn’t allow it (Japan/Afghanistan/Germany) but he could legally drink off-base according to the laws of the land, allowed but frowned upon. And yes, talk about a contradiction…he could fight the Taliban but couldn’t have a beer 
@twoinanddone Military personnel must be 21 to drink in the United States, including on base. There is some flexibility out of the country and they have the option of allowing it at 18 (not younger regardless of laws) but even then it was frowned upon. So yes, talk about a contradiction…you can fight the Taliban (my son served in Afghanistan at 19 years old) but you can’t have a beer.
Sorry, thought the first post was deleted?
2 states, New Hampshire and Wisconsin, are considering dropping the drinking age back to 18 for active duty military personnel.
I guess this is what I was thinking of. I believe they can drink on base in San Diego rather than have them go to Mexico.
^I didn’t know that, it makes perfect sense though doesn’t it?
Maybe it is a similar situation for OP (Installation Commander) to lower the drinking age, so the troop (visiting guests and D) can drink on base (San Diego) rather have them go out (to Mexico). 
I would be conflicted about knowingly serving minors in my home for legal liability reasons.
It was quite popular in one of my kid’s HS for kids to sneak out in the middle of the night. Someone would swing by the house where the sleepover was and everyone would pile in the car and off they went. D told me parents slept right thru it.
If I was confident the kids (< using that term loosely; these are college kids) would stay put, for real, and not over indulge, yes, I’d serve them.
These kids are coming in from out of state and flying. No transportation and nowhere for them to go. Plus our house is 100+ years old so you can’t take a step without the floors squeaking, we have a woofy dog, and the doors chime when they’re opened (thanks ADT). No one is sneaking out without waking up the household ; )
OP, if you know all the parents and it’s a situation where no one will be leaving the house, I’m not sure why you don’t just talk to their parents?
I would have no issue serving them nor would I mind my child being served.
Again, as these are adult women, I’m baffled by the calling the parents comments. To what end? When my D and S were 19/20, and visiting friends out of state, I would have been really confused by phone calls from someone’s parents asking me for my permission for, well, anything.
Agreed, the guest’s parents have no role in this. Why on earth would They? That would ensure the guests would not return, and may rupture the relationship with the hosts’ daughter. It would be completely inappropriate.
I imagine all these students are still dependents. Seems the parents still play quite a vital role in many aspects of their lives.
Again, everyone is different in how they feel about serving underage kids, illegal or not. But to furnish something illegal to my dependent without my knowledge is totally disrespect to me.
The financial status of these adults is none of your business, regardless of whether they are trust fund types or scholarship recipients. Your kids will play roles in your life forever-should your kids or their guests call your parents or siblings to report your drinking habits, or speeding? Adults have proper boundaries with other adults-which these are, regardless of how you feel towards them.
I’m a pretty toe the line person generally, but we often had kids’ friends on New Years and we always did a champagne toast. I always had sparkling cider handy, too and I saw plenty of kids take the sip and put the flute down. It is an acquired taste…We are remote and a destination and most of the kids and our friends that are staying over don’t even arrive until late after a day of skiing so never gave it a moments thought ;or worried someone would hop in a car at 1 AM t go who knows where. I did the same with my parents at holidays from the time I was a young girl. This is just an area where people have to decide for themselves how they are going to handle the situation. In my mind having a champaign toast is different from unlocking the liquor cabinet and telling a bunch of 18 years olds to have at it.