Is a little plastic Christ child usually... There are several traditions and dates for eating the Kings Cake.
Is part of Mardi Gras for some, or there is Rosca de Reyes (translates also to King's Cake) on Epiphany/12th night.
https://www.ksat.com/sa-live/2021/01...aten-on-jan-6/
There are other items baked into cakes in different cultures -- he's a breakdown of a lot of them and what they mean:
https://kingkingcakes.com/the-hidden...n-just-a-baby/