The Duke and Duchess of Cambridge and Prince Harry threw a tea party at Buckingham Palace for the children of men and women who died serving their country.
William, Kate and Harry welcomed more than 800 children and teenagers to the Queen's London home for the Party at the Palace.
The younger royals joined in the fun, with the Duchess and Prince Harry launching water balloons into the crowd with a catapult.
At one point, Prince Harry helped young spiderman, George Hinchliffe, 3, spin plates as Jack Rigby, the son of Fusilier Lee Rigby, who was killed by two Islamic extremists in Woolwich, watched alongside his mother, Rebecca, 34.
Mrs Rigby said: "We met Harry briefly while we were spinning the plates. He's a really nice guy."
Speaking about Party at the Palace, she said: "It's been a fantastic opportunity for both parents and children.
"It's great for the kids to meet other kids and to know there are others in the same boat, and it's a chance for the parents to meet each other and know you're in a safe environment and can ask advice of parents because they've been through things similar to you."
Entertainers included the ventriloquist Nina Conti, singer Jess Glynne and Britain's Got Talent-winning magician Lance Corporal Richard Jones.
The party brought together three of the issues William, Kate and Harry hold most closely to their hearts: bereavement, armed forces and young people.
In a speech to the young guests, Prince Harry said: "We're here to celebrate you and to remind you that we as a family, we as a nation, and we up and down the country will never ever forget about the sacrifices that every single one of you have made."
The prince continued: "You are all together, you are one community of people that have been through the same experiences and for that every single one of us here, all the organisers, the three of us the whole of our family and the whole of this nation, thank you so, so much for everything you guys have done.
"I can assure you that Buckingham Palace gardens have not seen this much fun, ever."
The tea party was organised by the royals as a special treat for the children and "to honour those whose mother or father have died fighting for their country", royal sources said.
William, Kate and Harry wanted to acknowledge "the fact that a number of young children have had to come to terms with the lost of someone very close to them at a young age".
The Duchess wore a dress by French fashion house Chloé which she had previously wore to a children's party during the Royal couple's tour of Canada.