Michelle Obama praises Kate's Huffington Post mental health edition
Mental health problems should no longer be seen as "taboo", the Duchess of Cambridge has written as guest editor of the Huffington Post UK website.
The duchess wrote that she and her husband, the Duke of Cambridge, "would not hesitate" to seek help if their two children needed it.
Her comments marked the launch of the Young Minds Matter editorial series.
US First Lady Michelle Obama said she was pleased Catherine was shining a "bright light on mental health".
The duchess has been guest editing the Huffington Post on Wednesday from a temporary newsroom in Kensington Palace.
Her role has seen her commission blogs, articles and videos from a selection of leading figures on the psychological well-being of children, including a blog from Mrs Obama about a man who suffered mental health problems after leaving the American navy.
The duchess also spent around half an hour in the editorial conference meeting, reviewing the content she had commissioned.
Later she met four children who had been filmed for motivational videos posted on Huffington Post, under the title Real Truth, about why adults should feel comfortable speaking to young people about their mental health.
The duchess, who is a campaigner for mental health and a patron of several related charities, wrote on the Huffington Post that during her work she had seen lives "torn apart, with devastating impacts for all involved, particularly children".
"What I did not expect was to see that time and time again, the issues that led people to addiction and destructive decision-making seemed to almost always stem from unresolved childhood challenges," she wrote.
"It became clear to me that many children - even those younger than five - have to deal with complex problems without the emotional resilience, language or confidence to ask for help.
"And it was also clear that, with mental health problems still being such a taboo, many adults are often too afraid to ask for help for the children in their care."
Catherine called for the stigma surrounding mental health to change and for it to be seen as "every bit as important" as the physical well-being of children.
She said she and the duke would also encourage their children, two-year-old Prince George and nine-month-old Princess Charlotte, to speak about their feelings and seek psychiatric support if they needed it.
"We hope to encourage George and Charlotte to speak about their feelings, and to give them the tools and sensitivity to be supportive peers to their friends as they get older. We know there is no shame in a young child struggling with their emotions or suffering from a mental illness," she wrote.
In a blog post Mrs Obama praised the duchess for being a "passionate voice" for mental health.
She wrote: "The Duchess of Cambridge has been a passionate voice on so many important issues, and I'm grateful that she is using her day as guest editor to shine a bright light on mental health, particularly children's mental health, and on the tens of millions of people who suffer in silence."
The first lady added that getting help should not be seen as "a sign of weakness" but "a sign of strength".
Children's charities said they hoped the duchess guest editing the Huffington Post would be a "turning point" in the way children's mental health is viewed.