He's a saint, for God's sake! He lives in Heaven, and so has transcended the limitations of time and space as we know them. He has all the time in the (other) world to do his work. When Einstein announced that time and space are relative, he was not saying anything completely knew. From at least the time of the Roman Empire theologians had recognized that time had no absolute existence, but was part of the current creation, and that outside of the latter, "before", "after", and "during" lack any concrete meaning. Furthermore, we have independent evidence that Heaven is timeless - in the data on near death experiences (NDEs).
I presume that most of my readers are aware of the basic outline of NDEs. After the out-of-the-body experience, and the dark tunnel, comes the meeting with a Being of Light. They are then given a life review, in which their whole life is displayed before them, and their actions evaluated against the criterion of love. (Shades of 1 John 4:7 !) The point is that NDEs last, by any estimation, only a few minutes at a maximum. Nobody is ever "out" long enough for a life review to take place in real time, nor does anyone come back feeling a whole 20, 30, or 40 years have passed. Rather, almost all report that the life review takes place in a timeless instant. Although it is well known that some physiological phenomena can mimic some aspects of NDE, I have never ever seen any naturalistic hypothesis to cover this particular aspect.
Once we get the time factor out of the way, it soon becomes obvious that all the other aspects of Santa Claus's activities are lesser problems.
Elves. Of course, there are all sorts of popular fancies about the nature of elves, and we are right to treat them with a grain of salt. But they definitely exist. This being the case, since we have no information on how many are involved with Santa, or how much of the year they work, or even the nature of their timeline, we have no reason to discount the tradition that they can get their job done in time for Christmas.
Making a List. No problem! I've already mentioned the NDE life review. Where he comes from, all our deeds are recorded.
Coming Down the Chimney. Well, no doubt he does that in higher latitudes where fireplaces are required. In these warmers climes he certainly has no difficulty gaining access to our homes. Most people don't realise that a glorified being would be more substantial than our earthly substance. The best way to explain this would be by quoting a work of fiction. In Out of the Silent Planet, C. S. Lewis has a Martian explain:
To us the [angel] is a thin, half-real body that can go through walls and rocks; to himself he goes through them because he is solid and they are like a cloud.Exactly! But we don't even need to go down that lane. There is good evidence that such things are possible with advanced technology even in our own level of existence. As I mentioned in passing in an earlier post, there are innumerable reports of UFO aliens walking through walls, and even taking their human abductees with them. If a visitor from outer space can do it, I can't see why it would be difficult for a visitor from Heaven.
Reindeer. Well, obviously earthly reindeer can't fly, but why should we assume they are earthly? Clement Moore described them - and we tend to forget this - as "eight tiny reindeer", so possibly he thought of them as fairy beasts. But my guess is that, like St Nick himself, they come from Heaven. After all, it wouldn't really be Heaven if there were no animals there, would it? And it would explain how they manage to operate on his timeline.
North Pole. I'm sure this is a misconception due to the fact that St Nicholas flies in from the far north. That just means that that is the site where he enters our plane of existence.
So, ladies and gentlemen, if your children start to fall under the spell of these cynical, rationalistic people, and tell you, "I don't believe in Santa Claus!", you can explain to them that all his exploits are perfectly explicable by known paranormal phenomena.