Prince William says it was a "balancing act" for himself and his wife to share details of the family's recent health challenges, including Catherine's and King Charles's cancer diagnoses.
In a rare and candid interview in Brazil, the prince said that "hiding stuff from them doesn't work".
He was responding to a question about how the couple had approached difficult moments with their three children — Prince George, 12, Princess Charlotte, 10, and Prince Louis, seven.
Earlier this year Princess Catherine said her cancer treatment was "like a roller-coaster", after revealing in January she was in remission.
The 43-year-old announced in March last year that she was undergoing treatment after tests following major abdominal surgery revealed she had cancer. She has never spoken publicly about the type of cancer.
King Charles also announced last year that he was receiving treatment for an undisclosed form of cancer, for which he is still receiving treatment.
"Every family has its own difficulties and its own challenges," Prince William said in an interview with Brazilian TV host Luciano Huck.
"I think it's very individual and sort of moment-dependent as to how you deal with those problems.
"We choose to communicate a lot more with our children, now that has its good things and its bad things.
"Sometimes you feel you're oversharing with the children [and] you probably shouldn't.
"But most of the time, hiding stuff from them doesn't work."
The Prince of Wales said explaining to the children "how they feel" and "why that's happening" could sometimes help give them "a bigger picture".
"They can relax more into it rather than being really anxious about 'what are you hiding from me?'" he said.
"There are a lot more questions when there are no answers.
"But it's always a balancing act, I mean, every parent knows that.
"How much do I say? What do I say? When do I say it?"
William spoke to Huck in Rio de Janeiro ahead of the Earthshot Prize awards ceremony earlier this month. He is the founder of the awards.
The prize, now in its fifth year, encourages inventors and entrepreneurs to develop technologies to combat global warming and mitigate its impact.
The prince later attended the 30th UN Climate Change Conference, known as COP30, in Belém.
William also said the couple's three children did not have phones.
He said Prince George may be allowed to have a phone with "limited access" when he attends secondary school next year.
"It's really hard," he said.
"It's getting to the point where it's becoming a little bit of a tense issue, but I think he understands why.
"We communicate why we don't think it's right, and again, I think it's the internet access I have a problem with.
"I think children can access too much stuff they don't need to see online."
Recently, the Princess of Wales warned that smartphones and other digital devices threatened the development of young children, in an essay published by Kate's Royal Foundation Centre for Early Childhood.
