If my boys were naughty I used to tell them that Santa would take a pressie out of their sack & replace it with a potato. One year they had been arguing a lot just before Christmas so on Christmas morning there were a couple of potatoes in their sacks!! I overheard the younger one say to his brother "I wonder what he took out. Next year I'm not going to be naughty all year!!"
oh this is brilliant. Daughter is a bit young at the moment but will remember. Did it work the following year??