Prince George, three, and 16-month-old Princess Charlotte were the centre of attention at a children's party held at Government House in Victoria, where the Cambridges have been based.
Charlotte, who was carried by her mum Kate, made a beeline for the colourful balloons as soon as she was set down. "Pop!" the little Princess said, pointing at the balloons while her big brother George looked around asking for "Mummy".
"Would you like a balloon, Charlotte?" William asked his daughter as he scooped her up in his arms.
George started to perk up after getting his hands on a water gun - and proceeded to quirt his little sister with water!
A group of military families, totalling 24 children and 24 adults from the Military Family Resource Centre, were invited to join the royal youngsters on their playdate - and the event, which Kensington Palace described as a "morning of surprises", proved a hit for all.
In pictures: George and Charlotte's sweetest tour moments
George and Charlotte sweetly bonded with other children their age, sharing their toys and happily playing games. Stalls had been set up in the grounds of the house, with everything from a petting zoo to a balloon stand.
A Nubian goat, two miniature horses called Honey and TC, a sheep, quails and a black and white rabbit were among the creatures that the children could pet. There was also a St John's Ambulance therapy dog, golden retriever and poodle cross, called Moose.
Charlotte had a whale of a time bouncing up and down on Moose, leading royal watchers to wonder whether the Cambridges' pet dog Lupo got the same kind of treatment at home.
The little Princess was also particularly taken by the black and white rabbit, and was pictured cuddling the furry animal and giggling.
Puppeteer Tim Gosley had the task of entertaining the children with a show, accompanied on guitar by Cam Culham, who was dressed in a red and patchwork outfit.
The youngsters also had a bubble machine blowing giant bubbles that kept them entertained while they waited for their royal visitors. A small tent was also set up serving refreshments including juice and tea and coffee for the adults; the paper cups fittingly had a crown design on them.
A palace spokesperson said: "The Duke and Duchess are really pleased to have this opportunity to introduce their children to Canada and it's great that they have the chance to play with other children while they are here."
This was George and Charlotte's second high-profile appearance during the tour. Royal watchers caught a glimpse of the siblings as they disembarked from the airplane and touched down in Victoria on Saturday.
While their parents have been carrying out dozens of engagement in different cities, from Vancouver to Bella Bella, George and Charlotte have stayed in the comfort of Government House where they are being looked after by their Spanish nanny Maria Teresa Turrion Borrallo.
The royal children have no doubt been spending time playing in the beautiful Government House gardens, which were spectacularly spruced up for their special visitors.
Even more exciting for the royal tots was the addition of a family of rubber ducks that were placed in fountains around the grounds, especially for the young Prince and Princess.
Stay tuned to HELLO! Online for the best coverage as our royal reporter Emily Nash joins the Cambridge family on this historic tour, and get ready for the next picture-packed issue of HELLO! magazine, out Monday