Prince George was pictured playing with a toy gun, toy knife and handcuffs as he had fun in the sun with their mother as his father played polo.
The Duke of Cambridge was taking part in the Maserati Royal Charity Polo Trophy at Beaufort Polo Club in Tetbury, Gloucestershire, on Sunday afternoon.
The family outing, which included Princess Charlotte, had came just a day after the Trooping the Colour ceremony to mark the Queen's official birthday which was followed by a gathering of the royals on the Buckingham Palace balcony.
The four-year-old prince is known to have an interest in the police.
On a visit to Finland last November, William met Father Christmas in Helsinki and was on a mission to present Santa Claus with a Christmas list from George, which featured one request – a toy police car.
At a reception in March celebrating the Metropolitan Police, one officer joked William's children could join the police cadets, to which the duke is said to have replied: "Well he does like the police at the moment."
Kate, dressed in a light blue open shoulder dress and wedges, was pictured sitting on the grass with George and Charlotte playing next to her.
Three-year-old Charlotte, sporting a sleeveless pink dress and holding sunglasses, was pictured skipping along barefoot.
She was also seen relaxing in Kate's lap and climbing up a bank with her mother.
George was dressed in beige shorts and a navy t-shirt.
Prince Louis, who was born in April, was not with his older siblings at the polo match.
The baby prince was also absent from the Royal Family's balcony appearance on Saturday afternoon.