My response is "Different families believe different things and that's okay!" or "they are real to those who believe"
Another provider I know has sent out a letter in the past basically saying that she understands each family has their own traditions, but the parents should make it clear to their kids that it's not their job to tell other kids there is/is not a Santa.
IME, even in families that don't "do" Santa, the kids still kind of know what Santa is (or supposed to be) and have just as much fun reading books, doing crafts, etc. I wouldn't change anything up if you have plans. I have moved away from Santa and company only because I find the kids get so, well frankly obnoxious this time of year (I know, I know, sue me) so I tend to focus more on giving with them.
True story - When I was first doing day care I had a family who didn't do Santa or the Easter Bunny, etc. Fine. At Christmas time this child stood up at the lunch table and told all the kids there was no such thing as Santa. I did the "he's real to those who believe" line. All fine and good, because of course she still got Christmas presents. Then Easter came and she did the same thing at the lunch table. I did the standard "he's real to those who believe" line. Monday after Easter when kids were talking about Easter baskets, who's in tears because she didn't get one
I always think of that when parents proudly proclaim "we don't do Santa/Easter Bunny/Tooth Fairy."