Question for photographers who have done Santa photos?

Just got done with a full week of Santa photos 2.5 hours per day with over 400 groups being photographed. I am just curious for those of you that have done it if you allowed parents to take pictures along side of you? If so, do you charge for the sitting? Officially we were not allowing pictures since we were doing the photo for free and they got a free 4x6, but it was almost impossible to enforce! Some people still felt the need to try and sneak in a photo for themselves. We were not out to make a profit because we like doing it for our city every year, but we try to cover our costs by having people buying a few additional prints. We even had a lady that came through the line 3 separate times to try and get 3 prints. Are people this cheap everywhere or just in our area? Kinda puts a damper on the Christmas spirit.