McFly’s Tom Fletcher and his sister Carrie Fletcher, wowed youngsters with a performance of On a Rainbow, the official song for the London 2012 mascots.

The exclusive event for schoolchildren yesterday evening (Thursday) was at Westfield Stratford City on the fringe of the Games site.

The McFly lead singer said: “This is an amazing opportunity and it’s something I’m very proud to be involved in.

“I wanted it to be fun for kids and a song that kids could remember and sing along to.”

The third instalment of an animated film, Rainbow Rescue featuring the mascots, Wenlock and Mandeville, which features the song was also premiered.

On the Rainbow is based on the mascots’ journey to the games and the young people they meet along the way.

Rainbow Rescue will be shown on 373 screens in more than 100 Odeon cinemas across the country before selected family films from November 25 to December 23.