The crowd was also played a video message from former England captain David Beckham.
After the Government committed to giving an extra £375 million to help feed the world's poorest children, Beckham said:
We've had good news. Earlier today the Prime Minister met with other world leaders and has made a real commitment to ending child malnutrition and hunger. There is more to do though and you can help.
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Accompanied by the Duke of Edinburgh, the Queen will attend the opening ceremony of the fifth session in the Holyrood chamber.
Ms Leadsom has received the backing of Ian Duncan Smith, the former work and pensions secretary.
The former shadow work and pensions secretary is considered a more viable candidate than Angela Eagle, a Labour source has told ITV News.