I am curious as to why some people put their Christmas presents under the tree before Christmas Eve. In my family we…

I am curious as to why some people put their Christmas presents under the tree before Christmas Eve. In my family we believed Santa came Christmas Eve and when we woke up Christmas morning we would have presents. It's a tradition I am going to continue with my son. His uncle puts presents out as soon as they're bought. Some times even in the shopping bags. And the kids are still told it's from Santa. Idk it ruins the magic to me and all of his children, even the 6 year old who I think is still in the "believing age range" doesn't believe. And hasn't believed in all the years I know her. These kids count each present and fight if one has more than the other. They also noticed last year when presents were removed and returned to the stores.

I am just curious. This is in no way meant to be rude, do you not tell the kids about Santa, does Santa bring Christmas Eve as well? What are your traditions?