Not necessarily Christmas traditions - but those come to mind.
For instance: My GF has two kids who are well past the Santa Claus believing age, but she started hiding Elf on a Shelf when they were quite little and they continued to insist on it.
The older and cleverer they got and the more hiding places she used up, the more of a chore it became. Hiding this guy every night was getting to be a royal pain.
One night she wrapped his little legs in a bandage and splatted him on the floor beneath the kitchen counter. Oh no! E on S had fallen broken his legs!!! When the kids found him, she fashioned a little bed and that's where he stayed for the rest of the Christmas season.
That was a couple of years ago and he still hasn't recovered. Laid-up Elf on a Shelf has become their new, easier tradition...
Pretty smart, don't you think?