Although there are etiqutette rules that are to be followed by the royal family, parenting styles and royal habits have changed over the years.
Traditionally, the young royals were expected to behave like adults while abiding the strict dress code. However, The Duke and Duchess of Cambridge and Sussexes have loosen it a bit to make their children's childhood more 'normal'.
According to a custom which goes back to the 16th century, royal parent's are not allowed to put their sons in long pants until they turn eight years old. Back then, young boys would wear gowns or dresses and then start wearing breeches when they turned eight. This transition was known as 'breeching', to signify a coming of age moment or a 'boy's step towards manhood'.
The dress tradition was eventually replaced by shorts around the 19th century.
"Its a very English thing to dress a young boy in shorts", etiquette expert William Hanson told Harper's Bazaar.
"Trousers are for older boys and men, whereas shorts on young boys is one of those silent class markers we have in England".
Prince George (8) wore a gown for his christening in 2013. From there, he started wearing shorts and rompers before transitioning to wearing his first set of trousers at the wedding of Prince Harry & Meghan Markle.
While Prince Louis (3), has not had to follow the traditions and has been able to wear trousers. He wore them on the red carpet at the panto with his family, and on the official Christmas card potograph released by the Duke and Duchess of Cambridge.