In her role as the royal patron of children's mental health charity Place2Be, the Duchess voices her belief that the nation's children should be: "supported through difficult times in their lives.
"This Children's Mental Health Week we want to support schools to prioritise the emotional wellbeing of their students, alongside academic success," she said.
"By ensuring every child is given the emotional support they need, we are giving them a firm foundation for the happy healthy future they deserve. Many of us are incredibly fortunate that the issues we face in childhood are ones we can cope with and learn from. But for some children, learning to cope with life's challenges can be a struggle.
"While we cannot always change a child's circumstances, we can give them the tools to cope, and to thrive. With early support they can learn to manage their emotions and feelings and know when to seek help. William and I feel that every child deserves to be supported through difficult times in their lives."
The Duchess filmed the video in Salusbury Primary School in Queen's Park, northwest London and is joined for parts of the message by four children who have benefited from support from Place2Be. The charity's second annual Children's Mental Health Week has the theme of 'building the resilience of children and their ability to cope with stressful situations'.
Find out more: Two-thirds children lack access to on-site school counsellor
Catherine Roche, chief executive of Place2Be, said: "Place2Be's work in over 250 schools and our training for school staff focus on understanding a child's behaviour and helping them to manage their emotions in a positive way.
"We are hugely grateful to the Duchess for helping to remove the stigma around children's mental health and for shining a spotlight on the value of supporting children in school from an early age."
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