Do you know the history behind the King Cake Parties?

A king cake (sometimes rendered as kingcake, kings' cake, king's cake, or three kings cake) is a type of cake associated with the festival of Epiphany in the Christmas season in a number of countries, and in other places with Mardi Gras and Carnival. It is popular in Christmas season in France, Belgium and Switzerland (galette or gâteau des Rois), Portugal (bolo rei), Spain and Spanish America (roscón or rosca de reyes and tortell in Catalonia), Greece and Cyprus (vasilopita) and Bulgaria (banitsa). In the United States, which celebrates Carnival in the Southeastern region, it is associated instead with Mardi Gras traditions.

The cake has a small trinket (often a small plastic baby, sometimes said to represent Baby Jesus) inside, and the person who gets the piece of cake with the trinket has various privileges and obligations (such as buying the cake for the next celebration).

I hope this information is helpful.