Kate Middleton has broken several royal rules since she joined the British monarch in 2011. Some of these are mundane things to ordinary people but not to the British royal family. A number of the protocols that the Duchess of Cambridge broke are also for the sake of her children.

In several instances, Kate chooses to be away from public engagements which are being carried out as official duties of the royal family members especially for Kate and Prince William who are future monarchs of England. In 2016, Kate decided to skip the presentation of a shamrock to the 1st battalion Irish guards for St Patrick's Day so she can spend time with her children. 

During her pregnancy with Prince Louis, she also decided to keep her royal duties to "a minimum." There were reports that Queen Elizabeth II was not pleased with the decision of Prince William's wife at the time.

Kate also doesn't mind breaking the rule that heirs to the throne aren't supposed to fly together. Prince William is second in the line of succession while their children, Prince George, Princess Charlotte, and Prince Louis are in third, fourth, and fifth, respectively. In the Duchess of Cambridge's family, William and their kids have traveled together on several occasions. 

"The Crown prefers that heirs to the throne don't fly together, in case of a fatal crash that would destroy their lineage," Vogue explained. 

Kate had also broken royal protocol when it comes to celebrating Christmas. Traditionally, the royal family spends Christmas at Sandringham House, the private home of Queen Elizabeth II. 

For the past years, however, Kate and her family spent the holiday at their home. In 2016, Kate hosted her parents and siblings for Christmas. The following year, Kate and William invited the former's parents to spend the holidays with them and their children at home. 

The Duchess of Cambridge also bent the rules when it comes to fashion style. Apparently, Queen Elizabeth has a rule that states the hemlines of female royals' outfit must be below the knee. However, during the Queen's 90th birthday celebration in 2016, Kate was clad with a light blue coat-dress that was slightly above the knee. She also donned in a short hemline maternity wardrobe in the past. 

Additionally, the Queen is also not fond of wedge heels. The Duchess of Cambridge, however, loves to wear them. 

There are other royal rules that Kate broke but there are also traditions that she and Willaim choose to keep. The couple has been adhering to the "no holding hands" rule when they are in public which her brother and sister-in-law are not keen on obeying. Since Prince Harry and his wife, Meghan Markle, announced their engagement in 2017, they have been spotted holding hands in public and there are no signs that they will stop doing it anytime soon.