Prince William said his wife Catherine is "doing well" following her cancer diagnosis.
The Prince of Wales made the remarks on a visit to St Mary's Community Hospital on the Isles of Scilly.
He was told about a new health and social care facility being built on Duchy land near the hospital.
The prince said his children George, Charlotte and Louis were "very jealous" of his trip, and said he may bring them to Cornwall later in the year.
He was given a letter by matron Lynda McHale, written by her granddaughter, that wished the Princess of Wales and the King well in their respective cancer recoveries.
The trip marks William's first official visit to the Isles of Scilly since becoming Duke of Cornwall, a title he holds in addition to his Prince of Wales title.
Ms Smith said: "I asked William about his wife Kate and he said: 'She's doing well, thanks,' and I suggested they might like to come for a visit and bring the children."
The Princess of Wales appealed for her family to have time, space and privacy when she announced her diagnosis of an undisclosed form of cancer on March 22. She said she had begun chemotherapy.
During his visit on Friday, William was given a card for his father the King - also a cancer patient - and Catherine by matron Lynda McHale, who said it was from her granddaughter "who wanted to wish his father and wife 'get well soon'."
As heir to the throne, William is Duke of Cornwall and receives an income from the Duchy of Cornwall, a portfolio of land, property and investments which owns much of the Isles of Scilly and nearly a third of residential buildings.
Friday's visit saw him using a spade to dig out soil on the site of what will be a new facility providing care and inpatient beds and a maternity suite at St Mary's.
The royal itinerary included a tour of St Mary's harbour, which is run by the duchy and handles everything from tripper boats to fishing vessels and cargo ships.
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PA MediaWilliam visited On The Quay cafe and ordered five pasties before stressing: "They're not all for me... but it does smell delicious in here."
"I was saying to the others, I can't believe the islands today when you've got weather like this - it's just beautiful," he said.
"I got in the sea yesterday which was good. I wore a wetsuit."
After leaving the cafe, William chatted to tourists waiting for boats to take them to various islands.
"I said to the team, 'do we have to leave today? Can't we stay a little bit longer?'," he told them.
When one woman replied that "you can do whatever you want" he said: "I wish, my family are very upset I'm here without them, My children will kill me if I don't get back."
Prince William's trip to Cornwall comes as the Duke and Duchess of Sussex begin a three-day visit to Nigeria.
