The candid photo was posted by @royalfashionpolice on Instagram and saw Kate looking gorgeous in a green patterned dress whilst enjoying the sunshine with her children who held their large flake 99 ice creams.
WATCH: Queen’s grandchildren and great-grandchildren lead the way at Easter service
Both siblings donned their school PE kit with George wearing what looked to be a football kit and Charlotte in a white polo and black shorts.
The off-duty sighting comes just days after the Cambridge family surprised royal fans and came out in force, including the Duke of Cambridge, for the Easter service at St.George's Chapel at Windsor Castle in Berkshire.
George and Charlotte looked fantastic on Sunday
The family were a picture as they stepped out looking marvellous in matching outfits for the celebrations.
Kate and Charlotte twinned in a stunning shade of pale blue, the Duchess in a calf-length coat dress and charlotte in a floral, pale blue tea dress with a Peter Pan collar.
The mother-and-daughter duo both added touches of navy blue to complement their looks, Kate with a deep blue pleated headband and matching shoes, and Charlotte with a navy blue knitted cardigan.
The Countess of Wessex and her family also attended the service
William and George also doubled up and both wore navy blue jackets and ties.
Their arrival at the service came just after the royal couple posted a special Easter message for royal fans on Twitter and Instagram.
The Duke and Duchess shared a photo that showed a piece of Kensington Palace-headed paper that had "Happy Easter" written in stunning calligraphy.
The Cambridges surprised royal fans
On Twitter, the royal couple wrote: "Wishing a Happy Easter to all our followers!"
The Countess of Wessex also arrived alongside her children, Lady Louise and James, Viscount Severn, and her husband the Earl of Wessex.
Princess Eugenie was also seen arriving at the chapel with her cousin Peter Phillips and his daughters Isla and Savannah.
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