Admit it, you've wondered.
It's not that Prince George is refusing 'big boy pants,' it's just a royal clothing tradition. Very royal, very 'upper-crust.'
Per Today.com, "“It’s a very English thing to dress a young boy in shorts,” British etiquette expert William Hanson told Bazaar (magazine). “Trousers are for older boys and men, whereas shorts on young boys is one of those silent class markers that we have in England.."
So you see the little price dress as his father did - in a pair of little shorts, often with knee socks, a jaunty belt and a sweater or tucked in shirt.
Today says, "... at age 3, young George is already more put together than most of us will ever be."
Hanson goes on to say that most boys graduate to full-length trousers at about 8. He said "the shorts-only tradition may stem from the antiquated custom of “breeching,” which dates back centuries in the U.K.
Traditionally, he said, young British boys were dressed in gowns for the first few years of their lives, until being “breeched” and graduating to short trousers."
In other words, 'breeching' a young boy helped others in the realization of the sex of the baby!