She may be a duchess, but even Kate Middleton knows that kids grow up in a flash — and she is still trying to wrap her head around the fact that her eldest is doing just that.

While the 37-year-old was visiting a center that supports young first-time parents and children in London on Thursday, September, 19, she happened to open about raising her own little ones. “She said children grow up so quickly and she can’t believe that [Prince] George is six already,” Chloe Koroma, 23, said after chatting to the Duchess of Cambridge. Kate shares George, 6, Princess Charlotte, 4, and Prince Louis, 1, with her husband, Prince William.

Prince George

We can’t blame Kate for realizing her baby boy isn’t a baby anymore, especially since he just recently started school again — this time with his young sister by his side. And this is something that has the little royal filled with joy. “George is over the moon that Charlotte is attending his school,” a friend of the royals exclusively told Closer Weekly. “Despite their different personalities, they are very close. George is extremely proud of Charlotte and loves to show her off.”

“Charlotte has met a lot of George’s friends,” the pal continued. “He is such a protective older brother that Kate knows he’ll keep an eye on Charlotte.” The future King of England has already showed a keen interests in numerous topics. “George is a curious child whose favorite subjects are geography, English and history,” the friend said. “Charlotte is more drawn to the arts. This year, she’ll take math, reading, French, music and ballet classes. “She loves dancing and is already talking about wanting the lead in the school’s Christmas play.”

Prince George Princess Charlotte

George — who recently celebrated a birthday — isn’t all about school though, he also has a knack for nature like his granddad, Prince Charles — and he proved that recently after enjoying his mom’s garden.

“George had such fun he didn’t want to leave. He loved exploring the garden and shares the same passion for nature as his grandfather [Prince] Charles,” a royal insider told Closer Weekly. “All the kids helped Kate and designers put the garden together. George, who is usually much quieter than Charlotte, made sure he had his say on the positioning of everything and choosing all of his favorite plants and flowers! He’s already showing the signs of being a great leader!”

It clear that George is growing up and becoming a smart young man!