Dressing up as Santa& little helper is a fun way to fool the kids. But you have to have the costume exactly right so as not to arouse any suspicions. Don& forget your elf shoes, which you can whip up out of leftover costume fabric in a few minutes.
Family Picture Craft-you could do this with pictures of the grandkids and trace out their hands. Or do one long picture with each family (yours Tom ect) in a grouping with a family pic as the last hand or do feet for your dad?