Guests at the event were reportedly praising the Duchess for her hands-on approach with the charity, and Kate continued to mingle with guests up to the last minute before the ceremony began.
"This is a wonderful, exciting opportunity to honour our young people and schools in such a wonderful setting, " said Place2Be Chief Executive Benita Refson.
She added: "The Duchess' total and utter belief in what we do and her commitment to children's mental health is incredible."
Kate is four months pregnant with her second child, and has become more involved with public events over the last few weeks, following several weeks of severe morning sickness.
Last week Prince William and Kate attended the Royal Variety Performance, meeting One Direction and McBusted, and on Monday it was confirmed that Kate and Prince William were set to visit New York City in December, for their first official engagement in the Big Apple.
The royal couple will take part in events which are close to their hearts, including tackling the illegal wildlife trade and meeting organisations which work with disadvantaged young people.