The Duchess of Cambridge has urged society to view children's mental health as being "every bit as important as their physical health" as she began her guest editorship of the Huffington Post UK.
Writing a blog to mark her role at the helm of the news site, she spoke about the psychological well-being of her own children Prince George and Princess Charlotte, saying she and William "would not hesitate to seek help for our children if they needed it".
Kate sat down to a morning conference in Kensington Palace with Huffington Post UK editor Stephen Hull, his staff and some of the mental health charities she is associated with.
She has commissioned articles, blogs and videos from leading figures in the mental health sector to raise awareness about the psychological well-being of the nation's children.
The Duchess wrote: "The mental health of our children must be seen as every bit as important as their physical health.
"For too long we have been embarrassed to admit when our children need emotional or psychiatric help, worried that the stigma associated with these problems would be detrimental to their futures."
The Duchess went on to say: "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."
From a newsroom set up in a palace drawing room, Kate used a computer mouse to launch the news website's top story or "splash" - a piece titled Never Too Young, about the importance of early intervention for those with mental health problems.
James Martin, a Huffington Post executive editor, asked the Duchess if she wanted to click the button to send the story live and told her: "This is the current splash which we have on the site which is your fantastic blog."
He added: "We've prepared what we call a splash, which is a hangover term from the time of newspapers when you'd splash a story on a newspaper and it's translated here into digital."
As she clicked the button Kate, who wore a Dolce and Gabbana skirt and shirt by Reiss, smiled and laughed.
The Duchess told all those in the room: "Can I just say a huge thank you to Stephen and obviously the huge team that's been involved in this, turning it around so quickly."
Mr Hull made the group laugh when he joked: "You've been a good boss."
The Duchess spent around half an hour in the editorial conference meeting, reviewing the content she had commissioned.
During her editorship she launched the Huffington Post initiative Young Minds Matter, which aims to encourage a wide-ranging discussion about children's mental health.
US First Lady Michelle Obama has written a blog for the site and she praised Kate for using her role as guest editor to "shine a bright light" on the issue of mental health.
The Duchess's editorship is the culmination of weeks of discussions with Huffington Post UK editor Stephen Hull and she has taken a close interest in the content published on his site on Wednesday.
Kate later joined four children who had been filmed for motivational videos posted on the news website under the title "Real Truth", about why adults should feel comfortable speaking to young people about their mental health.
The majority of the children have been helped by the charity Chance UK which provides mentors for youngsters with behavioural difficulties and the group were joined by their adult supporters.
In the messages the children talked about what they were good at and what they wanted to be, and Keira, an eight-year-old from London, made the group laugh when her long list of potential careers, including wrestler and boxer, were read out.
Kate praised the youngsters for recording the messages, telling them: "Your videos are brilliant, you really got your messages across. You should be very proud."
Peter Fonagy, chief executive of the children's mental health charity the Anna Freud Centre, joined the Duchess for the editorial meeting as it was announced that Kate had become his organisation's patron.
He said: "I think today can actually change the way children's mental health is viewed by society - it's that big.
"There's going to be millions and millions of people seeing children's mental health as front page news - it's been translated into 16 languages and viewed across the world.
"There's no way without Her Royal Highness a topic like this could have made this impact."
His words were echoed by Mr Hull, who said: "We feel like this is a turning point, this campaign has started, there's a movement that's started, we're leading it now but may not be leading it forever."