THE CHRONICLES OF NARNIA: THE LION, THE WITCH, AND THE WARDROBE (2005)
Nine-year-old Georgie Henley, who played Lucy, had a bucket on set that she called the "Potty Mouth Bucket." Whenever a cast or crew member swore around her they had to put $2 into the Potty Mouth Bucket.
Check out this great interview where she and James McAvoy (Mr. Tumnus) talk about it. I'd recommend watching the whole interview because it's very cute and funny and Georgie is an extremely smart 9-year-old, however, if you're in a hurry, skip to 3:05 to hear about the Potty Mouth Bucket.