Oh, the Santa thing -- this is my biggest parenting regret so far!
In my family growing up, we celebrated Christmas, but not really Santa Claus (my mother was from a different country and I guess Santa Claus wasn't such a big deal...)
My partner and I enjoyed playing Santa every year since our daughter was a baby -- staying up late after the kids went to sleep to wrap the presents and put them under the tree, filling their stockings, eating the cookies and carrots we left out, acting surprised and excited with them in the morning to find the presents! It was so fun to be able to create such a completely magical experience for our children.
When our daughter was in 1st grade, she came home telling us that someone at school told her Santa wasn't real. We acted confused by such a strange statement and assured her that of course Santa was real. Her reaction was so cute -- she pumped her fist in the air and said "I
knew it!!" Like, of course that kid was full of it and she couldn't wait to tell him.
In the summer after 2nd grade, she brought up the question a couple more times (other children whose families didn't celebrate Christmas and/or do Santa kept telling her it wasn't real,) and we kept telling her that of course Santa Claus was real -- but I was feeling more and more uncomfortable about how much more aggressively we were having to lie to her to convince her of this. And it was kind of difficult to on the one hand be trying to reassure her that there's no such thing as monsters / scary magic type things, but on the other hand insisting that Santa was real.
So, since she kept bringing it up, we assumed that she really already knew the truth and just wanted confirmation from us. So we decided that we would tell her. The second it was out of my mouth, I knew I had made a huge mistake. She
didn't really already know... her face just crumbled and she was devastated.

She spent the rest of the evening just sobbing and sobbing while we just held her. When we finally got her to sleep, we came downstairs and just sobbed and sobbed over what we'd done to her. Then I got on the internet and found all these various posts about families who did the "Santa Story" or the "Santa Game," and how devastated people had been when they'd learned that Santa wasn't real. Who knew???? The whole thing just blind-sided us. For days (weeks?) after you could see her face fall every time she remembered this new information. And then she made the painful realization that the Easter Bunny and Tooth Fairy must not be real either. It was just horrible -- the combination of finding out these wonderful, magical things weren't real and the fact that we'd been lying to her about it -- I think she really felt betrayed.
We thought we'd ruined Christmas for her. But she did end up having a nice Christmas this past year anyway. I think it was good that the truth came out quite far away from Christmas, so she had time to recover. And we made sure to go to just as much effort and include all the little details -- so I think that she found Christmas
almost as good as the ones when Santa was still real to her.
Anyway, just thought I'd share this story in case it helps someone avoid making the same mistake we made!