Sorry, OP, I didn't bother to read past the first page, so the PP are spot on with their advice.
Since my situation was over 30+ years ago, I think I am safe from getting castigated and run through the coals.
When my DD found some presents, I admit, I was sad/mad but she didn't know I knew she had hunted for them.
So, I decided we needed to have a talk, because I wanted to extend the Santa love and her brother was quite little. So, I fibbed a little.
I basically told her that now she is bigger she can know one of Santa's secrets. He cannot get all around the world with ALL the toys in one night. So, if parents are okay with it, Santa drops off some toys early. That way, when he comes on Christmas Eve, he can relax, have cookies and milk and do stockings and leave a couple of special items. I had to promise Santa that I would never ever peek at any of them, and I promised him my children were always on the nice list so they would never hurt him by peeking.
A couple years later, she knew there was not a "real" Santa, but then came the talk of the spirit of Santa and that she could not ruin it for her brother. If she did, she would get nothing but underwear for all the rest of her Christmases (with a wink). She also got to do the fun stuff, like going with me shopping for Toys 4 Tots and the angel tree. She never told him and with her being quite a bit older, she played along with an Oscar-worthy performance for several years.