We didn't really get raised with the whole Santa thing, sort of due to religious reasons and sort of due to the fact that I investigated everything all.the.time, and at three already had read about the story and de-bunked it. We knew the story of St Nicholas, and Sinterklass and Black Pete. There was always a present under the tree from Father Christmas, as the "spirit of Christmas" and sometimes there still is, even though we are all grown up now!
I don't actually know how my brother handles this (his kids are 10 and 3), but we always write on the tag From GG and MG, so there isn't really a shock coming, I don't think. Same with my sister (her kids are 11, 9 and 6 and one more on the way), but we have to send the presents up to her, so I don't know if she arranges anything.