I told my kids that the santa is real, but I have never threaten them with how santa is spying on kids to see if they behave and not giving presents to bad children. The funny thing is, my oldest daughter, to old to believe in santa and know very well he isnt real, "wants" to belive in him. She is prefectly rasional about it. It is the stories and the good feelings of exitement, fairytails, mysteries that she cheriesh.