They come from dramatically different cultures, and many don't even have a language in common.
But it doesn't matter to the 77 young people at a remarkable summer camp in Virginia, who each have a heartbreaking bond - they have all lost a loved one in a terrorist attack.
Project Common Bond started out as a way of bringing together children whose relatives died in the 9/11 attacks, but it's grown into an international project bringing together youths who have been scarred by terrorism.
When he arrived at the camp he didn't know anybody, but it didn't take him long to form profound relationships.
Project Common Bond is organised by Tuesday's Children, a non-profit group dedicated to serving the families of 9/11 victims. But the camp has, over the years, taken on a more international focus.
Losing a relative to terrorism is different because the tragedy plays out in public, said Fran Furman, director of counselling at Tuesday's Children.
She said: 'One of my friends doesn't speak English, and I'm still able to communicate with her and make a lasting friendship. I think that's amazing.'
In the mornings, campers attend classes and group discussions on peacemaking and conflict resolution.
This year's theme was dignity: how terrorists took it away; how they can reclaim it; and how they can encourage it in others.
Some have even chosen conflict resolution as a college major or career path based on their camp experiences.
Mijal Tenenbaum wasn't sure fun would be part of the experience when she attended last year's camp in Belfast, Northern Ireland.
Mijal, a 17-year-old from Argentina whose father was killed in the 1994 bombing of a Jewish community centre in Buenos Aires, said: 'I thought it would be weird, that we would be here and be awkward all the time because there would be this big elephant in the room that we would not talk about.
But when she arrived, she said, 'it felt amazing'.
Another gathering for children of 9/11 victims, called America's Camp, will be held in two weeks in Hinsdale, Massachusetts. But Project Common Bond is the only one with international participants.
The tenth anniversary of September 11 has not been a major focus of this year's camp, although a few campers are painting a mailbox that will be installed at the 9/11 Memorial at Ground Zero, serving as a symbolic receptacle for messages of peace from around the world.
The responses have been wide-ranging, said Monica Meehan McNamara, a family therapist and scholar who designs the curriculum for the camp.
Some said they were happy and wanted to celebrate, while others argued another killing wouldn't solve anything.
Marie Clyne, 21, a camp counsellor from Lindenhurst, New York, whose mother was killed on September 11, said she felt more relief than joy.
She said: 'It was kind of like, finally the bad guy is gone.' But she added: 'I see both sides.'
Sometimes the campers are forced to abandon their preconceptions. Project Common Bond includes both Israelis and Palestinians, and young people who hail from opposite sides of other conflicts.
He said: 'That was entirely new to me. I can't explain how powerful that was.'
Organisers hope to hold the camp abroad again next year, possibly in Spain. In the meantime, campers use social media to stay in touch throughout the year, and some even travel to visit one another.