The Duchess met those carrying out fundraising efforts for Shout, including 13-year-old Scout, Leo Street, who raised over £8,000 by sleeping outside for the entirety of 2021.
Kate joked: "There really isn't a big enough Scout badge for that. What you achieved is really inspiring."
"You must have had some impressive kit to keep warm," she said.
Leo, from Swanley, slept under a heavy-duty tarpaulin to shield from the extremities of the weather.
He told the Duchess his next fundraising adventure will be to cycle to Scotland during half term.
Kate also met Cassie Waters who began raising money for the text line after using the service herself when she suffered mental health challenges in 2021.