The Duchess of Cambridge has called for the "taboo" of mental health to be broken as she guest edits The Huffington Post for the day.
Kate wrote that for too long parents have been "embarrassed" to admit children need psychiatric care, worried of the stigma this may attract.
But she said it was time for our perception of mental illness to change, and said she and her husband, the Duke of Cambridge, "would not hesitate" to seek help if their children, two-year-old George and nine-month-old Charlotte, needed it.
Her comments came in a blog post written for The Huffington Post website to mark the launch of an editorial series called Young Minds Matter which discusses children and mental health.
The Duchess began campaigning on mental health soon after getting married and is patron of several related charities.
She wrote: "As was to be expected, I often heard some heart-breaking stories about lives that had been 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.
"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."
She called for this "to change" and for children's mental health to be seen as every bit as important as their physical well-being.
She added: "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 said parenting is hard enough without letting prejudices stop people from asking for help.
And as a mother herself, she said she and husband William will do all they can to encourage their children to speak about their feelings and seek psychiatric support if they need it.
She wrote: "Like most parents today, William and I would not hesitate to seek help for our children 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 acknowledged that seeking help is not always easy, and that poorer families can struggle to know where to get mental health support, and called for schools and communities to rally round and support children.
From a temporary newsroom set up in Kensington Palace, Kate will discuss articles, blogs and videos she commissioned to raise awareness about the psychological well-being of children.
And she paid tribute to the "extraordinary people and organisations" that have contributed to the mental health series.
She added: "Together, we have the chance to make a real difference for an entire generation of young children."