Even though Mary was the mother of the Son of God, she didn’t get a free pass in the diaper department. The Church teaches that Jesus was human in all things but sin. Thus, just like any other baby, he ate, digested, and yes, needed his diapers changed (or whatever passed for diapers in first-century Palestine). Unless Joseph was a dad who was radically ahead of his time, this stinky task would have traditionally fallen to Mary. It’s just one of the many ways that she, like any other mom, sacrificed her comfort to care for her child.