Prince William, his wife, said Prince George, 6, Princess Charlotte, 5, and Prince Louis, 2, enjoy the outdoors.
Kate also potted a sunflower for the family Delf, whose son Fraser, was cared for by the hospice.
The Duchess wanted to add a special touch to the event.
Kate brought a terracotta pot with other plants, in a recent royal assignment after Kate visited Fakenham Garden Center on her first public outing since lockdown.
In a message, the Duchess of Cambridge praised health workers for their efforts during the pandemic.
She thanked: “The amazing staff for all the work you do for the children: hospices across the UK
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Beside her majesty, mother of three, would have been to take part in The Key-giving Ceremony on June 29.
In the ceremony, His Majesty is offered the keys to the city.
The Queen is given the key by the Lord Provost to “the ancient and hereditary kingdom of Scotland.”
The result is a chain of canceled events, including the Wimbledon tennis tournament.
Kate honored the day by helping create a video for the official Wimbledon Instagram account.
The Duchess of Cambridge provided the voice over for the video.
In the recording, Kate says, “350 days, 14 hours and 12 minutes between the last bullet and when the next one was supposed to be.
“Over the years, your support has shaped this historic event.
“No matter the time of day or the names on the dashboard, you’ve always been there, rain or shine.
“This year, alas, things are very different, but we will do our time belly down until we sit on the edge of our seats again and celebrate again.
“So when the time is right and we open the doors, we will be there again and it is worth the wait. “