This is a tradition that my mom always had us do while I was growing up. Every year we had an Advent manger. It is a basket that baby Jesus will be placed in on Christmas day, but it is up to the kids to make sure that baby Jesus has a nice soft bed in which to sleep. Every time they get caught doing a good deed or they obey cheerfully or share willingly they are allowed to put a piece of "straw" (yellow yarn) into baby Jesus' bed.
So far, they have really taken to this idea. Yesterday, Jonathan was begging me to give him more chores to do so that he could put more straw in the manger! He cleaned up their playroom all by himself (and it was desperately in need of being picked up) just so he could get more straw. Now I know why Mom did this little project every year! ;)