Place2Be's founder, Benita Refson, told the Mail on Sunday the charity was delighted to have Kate's support again. "The Duchess' involvement with the first-ever Children's Mental Health Week last year made a huge impact and her video message of support reached millions across the world," she said.
Kate will also be guest editor of the Huffington Post UK's website for a day next month to highlight the importance of mental health.
The charity role marks the Duchess' return from maternity leave following the birth of her daughter, Princess Charlotte, last May.
And her work has started to draw comparisons with that of her late mother-in-law.
Echoing Diana's secret visits to charity centres and hospitals, the Duchess has made similar private visits to meet children affected by mental ill health - an attempt to offer support without attracting the media spotlight.
An aide said: "The Duchess spent a large chunk of last year on maternity leave. She will continue to focus on her family but this year she will be doing more engagements and mental health is going to be a big cause."
In an address to head teachers for Place2Be last year, the Duchess explained her decision to support the charity: "I often get asked why I decided to spend time highlighting the mental health of children. I know that 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."
The Duchess will reportedly continue her work with other charities, including The Art Room, SportsAid and East Anglian Children's Hospice, but looks to be focusing on children's mental health.
Kate has also joined her husband, Prince William, to promote World Mental Health Day for the charity Mind in October.
- nzherald.co.nz