Speaking confidently for about three and a half minutes at a gathering of teachers brought together by the charity Place2be, she said, "I was lucky. My parents and teachers provided me with a wonderful and secure childhood where I always knew I was loved, valued and listened to.
"But of course many children are not so lucky. Since beginning my work in areas like addiction, for example, I have seen time and time again that the roots of poor mental health in adulthood are almost always present in unresolved childhood challenges."
Kate has been working on the speech – which she wrote herself – for a week, a palace source tells PEOPLE. While she has only rarely made public speeches, they say she will do so more as opportunities arise.
The royal mom, in a gray dress by Matthew Williamson that she has worn before, added, "I am sure you will agree that all children deserve time, attention and love from the adults in their lives. These basic qualities are so much more valuable than the always-changing material and social concerns that can seem so important to young people.
"As today's theme reminds us, many children – even those from stable, happy homes – are finding that their heads are just too full. It is our duty, as parents and as teachers, to give all children the space to build their emotional strength and provide a strong foundation for their future.
Earlier she was praised for the "unique role" she plays as a "champion to highlight the importance of children's mental health," by the charity's chief executive Catherine Roche.
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In her speech, Kate also noted, "Many will arrive through your school gates feeling a real lack of love and devotion in their lives. This often leaves them feeling insecure and without confidence and trust in the world around them. That is why your work is so important."
"Parents, teachers and other school staff need the tools to help these young people early in their lives. And the earlier, the better. It is proven that early action prevents problems later in life.
"Imagine if everyone was able to help just one child who needs to be listened to, needs to be respected, and needs to be loved – we could make such a huge difference for an entire generation."
Place2Be is one of the first charities that Kate took on, and signaled the beginning of her championing of needs of vulnerable children, which has led to her deep immersion in the campaign to highlight, and improve services in, the issue of mental health.
Early intervention of the problem has been her main focus and much of that is via schools, where Place2Be has centered its activities.
She was joining head teachers from around the U.K. who were discussing the key issues and latest thinking on the role that schools can play in tackling mental health problems early in life and who will share ideas and expertise to help, what the charity says, "build children's emotional resilience."
Meanwhile, Kate's husband Prince William was in Sutton, in the southwest suburbs of London, earlier learning about the cancer research and clinical trial facilities at the Royal Marsden. He is President of the hospital trust and has observed operations in the past. Today, he was seeing how new cancer treatments are carried out and was meeting leading clinicians and patients participating in trials.