Kate wore a light yellow See by Chloé dress (currently selling for $460) and gray Monsoon wedges for the event while Harry and William kept things slightly casual in blue sport jackets and white button-up shirts. The royal trio chatted with children at different activity stations at the party. Kate chatted with a group of girls while Harry played around with several kids.
Kate also took part in launching a giant slingshot from the palace’s steps and giggled along with William and Harry during the festivities.
The celebration honored the children of service members who have died while in the armed forces. “Their Royal Highnesses have arranged the event as a way to acknowledge and honor the fact that a number of young children have had to come to terms with the loss of someone very close to them at a young age,” a statement from the royals’ office at Kensington Palace said.
“The Duke and Duchess and Prince Harry hope the event will provide an opportunity for these children to broaden their support networks amongst other families with similar experiences.”
Prince Harry made an emotional speech to the party, telling the guests, “Today was organized to celebrate you guys. We’re here to remind you that we as a family, and as a nation will never, ever forget the sacrifices that all of you here have made.
“We wanted to give you an opportunity to know that you are part of, sadly, a very large group of fantastic people. The three of us, and all of our family, wanted to thank you so, so much for everything you’ve done.
“I can assure you that Buckingham Palace gardens have not seen this much fun, ever.”
William and Harry, who are marking the 20th anniversary of the death of their mother Princess Diana this year, ensured there were organisations that support families and children dealing with loss were also in attendance.
Child Bereavement UK, of which William is patron, Scotty’s Little Soldiers, Winston’s Wish and the armed forces charity SSAFA were there alongside Full Effect and Coach Core, which hosted workshops in beatboxing, breakdancing and other sports on the lawns.
Both William and Harry have recently been opening up more than ever about the loss of their mum, with William telling the BBC last month, “People say shock can’t last that long, but it does. You never get over it. It’s such an unbelievably big moment in your life that it never leaves you, you just learn to deal with it.”
And on April 30, Prince Harry comforted a pair of siblings who lost their mum in a bicycle accident.
“He just told us everything will be okay, even though everything seems really bad at the moment, it will get better,” 11-year-old Emily Briggs told The Telegraph.
At the party, Harry met with Jack Rigby, 6, the son of Fusilier Lee Rigby who was murdered in 2013 by Islamic extremists outside the Royal Artillery Barracks in Woolwich, south London.
Jack’s mother, Rebecca Rigby, 34, told reporters, “It means so much that the royals put this event on and are showing us their support. It’s so important for Jack and all the other children here to know they are not forgotten – that they’ve not gone through all of this to be forgotten, that they’ve got their support.
“It’s also so important for Jack to be able to speak to other children and know that other children have gone through the same thing as he has.”
The playful prince also had a go at plate-spinning with George Hinchcliffe, 3, who had dressed as superhero Spider-man for the party.
His father, Captain Richard Hinchfliffe, who served with the Royal Armoured Medical Corps, died in an accident as a civilian in 2015 shortly after leaving the RAMC.
His mother, Abigail Hinchcliffe, said it was “very emotional” to be at Buckingham Palace and watch her son playing with Prince Harry.
Also invited was Jamie Molyneux, 18, and his younger brothers and sister, Arron, Charlie and Bethany. Their father Lt Cdr Ian Molyneux was murdered in 2011 by Ryan Donovan, a junior member of the royal navy while on board the nuclear submarine HMS Astute.
Lt Cdr Molyneux received a posthumous George Medal for his actions which prevented others being killed.
Mr Molyneux, from Wigan, who was 13 when his father died, said it was “comforting” to know his family had not been forgotten. “The Duke of Cambridge wrote to us soon after my dad was killed. It was very touching. He said he understood what we were going through as siblings, with his experience losing his mum,” he told reporters.
“I had two choices to make. I was either going to go off the rails and end up in prison or accept what’s happened and do the best I can.”
Mr Molyneux is following in his father’s footsteps, and passed out of Welbeck Defence Sixth Form College, Leicestershire, last year, with the award for best naval cadet.
Also among the guests was Honey Doherty, 10, whose elder brother Jeff died when she was a baby when he was killed serving in the Parachute Regiment in Afghanistan.
“I’m really happy but I’m also really grateful because of what a hero my brother is, and I wouldn’t be going there if it wasn’t for him,” she said. Private Doherty was shot dead in Sangin in 2008, aged 20.
The party ended with a special display by the RAF Falcons, the parachute display team, who parachuted over the roof of the Palace into the gardens to delight of the children.
This story originally appeared on PEOPLE.com.