The competition asks Blue Peter viewers to design a sculpture to go into the royals Back to Nature garden when it arrives at RHS Wisley in September.
In her latest public appearance, the mother-of-three - who is fresh from designing her woodland garden for RHS Chelsea Flower show - can be seen pond dipping, planting and team den building with local kids and the shows presenter, Lindsey Russell.
Duchess Kate also discussed her love for outdoor activities, telling Lindsey: "It encourages creativity, confidence and even a short amount of time—10-15 minutes outside—makes a huge difference to physical well-being but also to our mental well-being.''
Last month, the 37-year-old shared a personal video highlighting the importance of nature within her own family when she and husband Prince William and all three of their kids—Prince George, 5, Princess Charlotte, 4, and Prince Louis, 1—visited her "Back to Nature" garden in London last month.
WATCH KATE & HER FAMILY HIT THE OUTDOORS HERE!