The royal couple, who enjoyed a casual kickabout at Bacon's College in South-East London, were joined by Prince Harry for the launch of the scheme which aims to turn talented teenagers from impoverished backgrounds into the next generation of sports coaches.
The future Queen, wearing a £35 patterned white and beige Hobbs dress with matching beige wedges, played a game of table tennis with one teenage girl before removing her sandals to referee a judo match.
Prince William, looking smart in a white shirt tucked into navy blue trousers, joined in with a group of young boys practising their football skills, despite later describing himself like a "a giraffe on ice" on the pitch.
Prince Harry attempted to play basketball but reportedly failed to get a single ball through the hoop.
The Royal Foundation, run by the Duchess and the Princes, will fund the pilot "coach core" project.