Kate Middleton is eager to have another baby with Prince William now that their youngest son and "mommy's boy" Prince Louis is a bit older. A source said that the Duchess of Cambridge wants another baby who will grow up together with her other kids -- Prince George, 6, Princess Charlotte, 4, and Prince Louis, 18 months.

The source revealed to Us Weekly that the youngest Cambridge royal is now playing together with his older siblings. They paint, bake and build things while their parents watch them interact.  

George, Charlotte and Louis bicker like normal kids as well. For the most part, however, the children get along well and their parents are only happy to see them grow up with different personalities.

If Prince Louis is the "mommy's boy," Princess Charlotte is a confident young lady who loves all of the attention. Prince George, the third in line to the throne who could one day become the King of England, is more reserved than his little sister. Like a big brother, he also looks out for his siblings and is showing signs of leadership.

At 37 years old, Kate Middleton could still get pregnant with baby number four. According to royal historian Juliet Rieden, the Duchess of Cambridge would love to have another baby but it might be unlikely at this point.

Rieden said, via Daily Express, that the Kate used to talk on and off about having more kids with Prince William. However, the Duke of Cambridge doesn't seem eager to add to the brood. More than once after the birth of his kids, Prince William relayed that he's having sleepless nights taking care of the babies.  

The Cambridges might also be holding off on another baby since Kate has a challenging experience carrying a child to term. The duchess suffered from an extreme case of morning sickness called hyperemesis gravidarum in all of her pregnancies, which confined her to the bed for the first trimester. Would she be willing to endure this for a fourth time? 

Meanwhile, rumors that Kate Middleton is pregnant again surfaced when she and Prince William visited Pakistan. Apparently, they had a doctor join them during the trip which has never happened before. This sparked talks that the doctor was there to ensure that Kate would be alright since she is in a delicate situation with a baby in her womb. However, palace sources said that, since the travel to Pakistan was their more complex tour arrangement to date, Prince William and Kate Middleton decided to bring a doctor.