As they should have! ;) Meanie.
When my oldest learned there was so Santa (jolly guy in red suit who was able to travel the world in a sleigh pulled by reindeer, giving gifts all in one night), I made her promise not to tell her younger sisters. Plus, she was the big girl now and could help wrap gifts and prepare for Christmas, lol. She was part of the adult world and shared a secret. And, her helping wrap gifts was huge since I hate wrapping gifts. Then the next kid, a year younger, learned there was no Santa, so she was part of the magical secret for her younger sisters...and she could help wrap gifts, lol, but she’s still an awful “wrapper” just like her mom. Then the 3rd kid learned there was no Santa but the youngest couldn’t know...They all kept the secret and didn’t ruin it for their younger sisters.
This year, the youngest knows there’s no Santa, and being the youngest, she’s not happy about that although she has helped wrapped gifts.
Yep. Each of my children became “Santa’s Helper” when they figured it out. Of course, they no longer get the extra “Santa Present”, but Mom still comes through. :)