Prince George plays with toy gun at the polo

The little girls, who are George and Charlotte's second cousins, are clearly very comfortable with Catherine's children, having appeared on the balcony with them at the Trooping the Colour the previous day, where Savannah got a laugh from viewers after she was caught putting her hand over George's mouth, having clearly had enough of his rendition of "God Save the Queen".

Meanwhile, Princess Charlotte did handstands, sending her mother into a fit of giggles.

After the pictures emerged, several people took to Twitter to voice their outrage and suggest that the royal family should have been more mindful about the toys they give Prince George and Princess Charlotte.

Four-year-old George, dressed in beige shorts and a navy top, was seen playing with a colourful Slinky and taking aim at his friends with a toy gun.

"Sad to see George playing with a gun with the whole country has a gun/knife crime situation", another said.

Charlotte, 3, wearing a pink sundress and adorable sunnies, was spotted running around barefoot on the field with her brother and practising her tumbles.

Low-heeled wedges and a casual dress meant Catherine had no problem bounding down the hill after Prince George. The young royals played with their cousins Savannah and Isla Philips, who made a splash on the Buckingham Palace balcony the previous day.

Prince George of Cambridge and Princess Charlotte of Cambridge attend the Maserati Royal Charity Polo Trophy at the Beaufort Polo Club on June 10, 2018 in Gloucester, England.

Sitting on a grass slope together, Savannah, 7, was pictured with her arm around Charlotte.

Prince Louis, who was born in April, was not with his older siblings at the polo match.