Mom and Dad were pretty good. And I am pretty gullible. We believed for a long while. I think I finally found some unwrapped gifts one year. But still wanted to believe so made excuses. I finally figured it out when Mom said "I know you don't believe in Santa, but your sister still does, so don't tell her, ok?"

They would pick out a special Santa paper for each kid. All the gifts for one kid would be wrapped in that paper and on Christmas morning they'd be separated into piles with our stockings in front of them so we knew whose gifts were whose. So no handwriting to give it away. And no wrapping paper to do so either.
The gifts were kept in layaway or the storage unit until the 23rd or 24th.
Stockings are stuffed with an orange in the toe, small toys, candy, a new toothbrush, and nuts.
Santa came through the door, because we had no fireplace. And the yard had no grass to check for muddy prints (no snow, lots of rain). It was a Japanese rock garden out front and a paved area out back.
And if a bar code was accidentally left on the gift? He obviously did some of his gift-giving from stores because otherwise he'd have to make a lot of toys. And why should he have to make them all when there are so many people who do that already?
At 25 and 22 we are both unmarried so come home every Christmas, even when we are not living here. We still get a huge pile of Santa presents. We pick out our own Santa paper if we happen to be there when it is bought.
And now that we're older, mom doesn't have to buy her own "Santa presents" (apparently dad was next to useless at gift-giving). But it usually means "on no, we forgot to get mom Santa gifts! Quick! Re-wrap some of her other gifts in Santa paper!" Which isn't that bad because she tends to get more gifts from us than anyone else does.
I do get a little sad sometimes because mom and dad never get me anything for Christmas anymore

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I usually don't tell people this though, because I get funny looks about being this old and still having a full-out Santa gift exchange every year. And I feel silly, but I enjoy it.