Thirty years ago a young, but not small girl was bribed. The payoff to influence participation in a school Christmas play was a McDonald's happy meal. Acrimonious participation behind her, happy meal in front of her, said girl did not eat. Concerned mother ushered young girl into restroom only to discover that young girl had a little known virus called the chicken pox.
Little has changed in 30 years. Well, except for this time the young girl is now the mother of a young boy. And the boy didn't have chicken pox. And there you have it, a tradition is born.