I had never thought about getting my children to help Santa all year long, but it's been--well--Magical!
We created a Christmas Magic Meter, and I hung it on our fridge. It's got a movable hand. I will quietly adjust it up or down depending on the situation.
They love to check the meter. When it goes down, they ask what they can do to help. Sometimes we sing and dance. At other times, I assign a quick chore that they can do.