While the royals are currently enjoying being a family of five, the question remains as to whether the pair would decide to their family again, though a source told Us Weekly that another child is unlikely.
"They are absolutely thrilled with having three [children]," the source said. "They are soaking up every minute they can. Their dream was always to have three kids. Kate knew she wanted a third not long after having Charlotte, but this time around they seem very content."
Still, the insider added, "Never say never!"
A friend of the couple told PEOPLE that Middleton "is one of three siblings, and it's a good family size. Boy-girl-boy is pretty cool as well."
Since Louis' birth, he has been bonding with various members of his family, including big sister Charlotte, who is already close to her baby brother.
"Charlotte is really enjoying having a younger brother to play with," a royal insider told Us Weekly. "She's taking her big sister duties very seriously. She won't leave baby Louis' side."
The source added that Prince George, 4, is "protective" of his new sibling, as is Charlotte.
"Charlotte is just like him," the insider said. "They have a great bond, and a similar connection is growing between Charlotte and Louis."
Charlotte celebrated her third birthday on May 2 and was made to feel special all day long. At Willcocks Nursery School in London, where she attends Monday through Thursday, she was given a cake to share with her classmates, and once at home after her half-day lesson, she was celebrated by her parents.
"They like to make a fuss on the kids' birthdays," a source said. "There is always cake, her favorite dinner and a lot of presents."
While the 3-year-old is "definitely a girly-girl," according to the insider, "She's very confident." The source added that Charlotte is "not afraid of a grazed knee and it's not going to stop her from running around. She moves at the speed of light!"
The family is still settling in to live as a party of five, though they resumed some royal routine on Wednesday when William returned to work after the birth of his son, with the royal stepping out to open a London Bridge station.
Photo Credit: Getty / Max Mumby / Indigo