Despite all the rules surrounding a royal birth announcement, there is, according to a spokesperson for St. James's Palace quoted in Vogue UK before Prince George's christening, no strict royal protocol when it comes to a royal baby's baptism and that "the way in which the prince is baptised 'depends entirely on the family.'"
Before 2013, Vogue UK reports, royal babies were typically baptized "by the Archbishop of Canterbury in the Music Room of Buckingham Palace," but when Prince George was baptized in October 2013, USA Today reports that, in a break with past practice, the ceremony was held in the Chapel Royal at St. James's Palace. Additionally, there were only 22 people in attendance, with a royal guest list that only included the Queen, Prince Phillip, Prince Charles, Duchess Camilla, and Prince Harry, a ceremony that was "kept uncharacteristically small, in a shift away from the larger ceremonies that his father and grandfather enjoyed at Buckingham Palace," according to CNN.
In another break with tradition, William and Kate chose close friends and family members — as opposed to foreign dignitaries — to be George and Charlotte's godparents (Prince Charles' godparents, by contrast, include "two kings, one queen, one princess, and one prince," according to USA Today). For Princess Charlotte's baptism, The Guardian notes that the family chose a church in Sandringham, Norfolk — a town in the English countryside about two hours from London, where the royal family has an estate.