My son is 8 and my twin girls are 5. My kids are full on believers in Santa Clause. It takes a lot of work to make it more believable.
On Christmas Eve we open all gifts from mom, dad, grandparents etc. The kids go to bed with nothing under the tree.
We have canvas sacks with their names on them and put a bunch of smaller toys, games, inside these. They usually get 2-3 bigger gifts from Santa and a full stocking of candy and trinket type things (bouncy balls, hot wheels etc)
Also no name tags ( kids learn your hand writing), no packaging ( why is it packaged like it came from a store? Don’t elves make the toys). Everything is ready to play. Batteries are charged. Assembly is complete. My kids fully believe.
Mom and Dad get stockings full of our favorite snacks and mini bottles of alcohol