"They are very much a family of sailors now," a source declared. "Kate has always been a competent sailor and William’s pretty good too. They have enjoyed some wonderful time on the coast this summer sailing and showing the children how to steer and sail a boat."
The source noted that the children "love the water and the two eldest are good swimmers and had no qualms about jumping into the sea even if it was a bit fresh."
"The kids were all running in and out of the water with their dog and spent hours playing in the sand," added the onlooker. "They are clearly a family that love being outdoors and in nature. It was lovely to see them playing so freely and not being bothered by anyone."
The family-of-five closed out the summer season by taking a trip to Scotland, where Queen Elizabeth is staying at her Balmoral estate.
"They always enjoy going up to Balmoral, they love the outdoors and walking in the hills and spending quality time with family," an insider said. "It’s where William spent a lot of his childhood and it’s important to him that his children experience what he did as a young boy."
The vacation has become an annual tradition for the royal brood, with the insider calling it "one big sleepover."
Following the visit, the Cambridge kids will go back to school in London after doing virtual classes last year.
George and Charlotte will return to Thomas's Battersea Prep School, while Louis will attend Willcocks Nursery School.