When an older child starts understanding how family magic is created, that does not have to end the tradition.
Invite them behind the scenes
Let the older child help with the part of the activity that younger siblings should not see.
Give them a real responsibility
They can manage the surprise, photograph the night, read the story, or help younger children decorate.
Protect younger siblings without making the older child perform
The role should feel like trust, not a job they are forced to do.
Let the tradition mature
With The Tomte Cake, an older child can move from searching for Tomte to helping create the mystery. That shift can make the tradition feel age-appropriate again.