'Considerable power' to family portrait
Those who chronicle the lives of the Cambridges now know that balloons are the way to a 16-month-old princess's heart and Charlotte's first public utterance was to use the word "pop".
And for toddler George there was much fun to be had squirting bubbles at his father - even if he is a future king of Canada and the UK.
Considerable column inches are generated from such offerings. The power of the images is considerable.
The children personify the future of the Canadian monarchy in a country that may, one day, chose a different path.
There's no sign, at the moment, of that being the desire of the majority of Canadians.
George and Charlotte, on display, will not become an everyday occurrence.
William and Kate are determined their children grow up in private and not in public. This party will attract global attention because of its rarity value.