The royal siblings posed for a photo together outside of Kensington Palace before heading off to school with their parents.
This is the first time the Prince George and Princess Charlotte will attend the same school. Previously, while Charlotte was enrolled at Willcocks Nursery School in London, George was a pupil at Westacre Montessori School Nursery in East Walton, which was closer to their family home at the time.
Prince William drove the family of four—Prince Louis stayed home—to school. Later, he told Lower School head Helen Haslem that his daughter is "very excited" about her first day.
Stylish mum Kate Middleton slipped into a floral, Michael Kors dress for the occasion, the same piece she wore to Prince Harry and Meghan Markle's wedding rehearsal.
At school, the royals will ditch their titles of Prince and Princess. They'll go by George and Charlotte Cambridge. After all, their parents are the Duke and Duchess of Cambridge.
During her first year, Charlotte will be encouraged to "play and explore," according to the school. "Make choices and learn to have a go and persevere; be creative and solve problems; form good relationships; be safe, secure and happy."
But, perhaps most importantly, she'll follow their golden rule: "Be kind."
At the $23,000-a-year private school, George, 6, will learn more about core subjects including math, English, science, history and geography. Each day, he'll bring home 10 minutes of reading homework.
The cheeky 4-year-old has joined a class of about 20 students.