Six years ago, a group of teenagers from the Rosebud Sioux Tribe ventured 1,500 miles from South Dakota to Pennsylvania, placing candy on the graves of children buried on the grounds of the former Carlisle Indian Industrial School.

The youths sang prayer songs, wept in grief and anger, called out the names of the sons and daughters who died in a U.S. government effort to force Native Americans to assimilate into white society.

They knew the children’s spirits heard them, the teens said, because as they left the cemetery, the summer air filled with swarms of glowing fireflies.

Today those teens are grown to young women and men. And this week they returned, helping to claim the remains of nine tribal boys and girls and escort them home to the vast grasslands of the Rosebud reservation.

“We were just kids. Our voices cracked,” said Christopher Eagle Bear, then a 17-year-old high school senior, now a 23-year-old wildland firefighter. “A lot of leaders, a lot of young leaders, have been built out of this.”

That first visit to the cemetery, on the campus of what is now the Army War College, passed largely unnoticed except by those who were there and those they told afterward. But as word spread, it helped ignite a rights and repatriation movement, one that’s gained new urgency amid the discovery of more than 1,100 unmarked graves on or near the campuses of three former Canadian boarding schools.

Interior Secretary Deb Haaland, whose great-grandfather attended Carlisle, has launched a Truth Initiative to identify known and possible student burial grounds and to determine the names and tribes of children in them.

An Interior spokesperson had no information on how Carlisle might fit into the inquiry.

But this disinterment produced disquieting findings — the discovery of a second set of remains in the same grave as Maud, also called Little Girl, the 16-year-old daughter of Chief Swift Bear. The Army also said that another grave contained an additional second vertebra, a bone that sits high in the neck. Those remains were being reburied in the cemetery.

That means the four cemetery disinterments to date have produced three unidentified sets of remains. In the first in 2017, a Northern Arapaho child, Little Plume, was missing from his grave. Buried there instead were two unknown remains, which were reinterred. Little Plume’s remains were later located and returned to his family in Wyoming.

At a formal return ceremony near the cemetery on Wednesday, tiny caskets were officially transferred into the custody of the Rosebud Sioux. Haaland spoke. And so did the youth leaders.

“They’ve continued to be guided by traditional ceremonies, and respecting that guidance from the spirits and the ancestors,” said Micah Lunderman, 37, a Rosebud Sioux youth counselor and mentor who helped organize that first trip. “How much more prouder can we be of them?”

Her son, Josh Iron Shell, was 14 on that initial visit, a boy trying to figure out what he wanted in life, determined to join in causes larger than himself. Today he’s almost 21 and about to start his fourth year at the University of Denver, where he studies psychology and criminology.

Iron Shell wants to work providing mental-health services to people in his home community, partly to help them heal from traumas inflicted at the hundreds of church- and government-run schools that sprang from the Carlisle model. The repatriation — the largest in a series that’s seen 21 children returned to tribes since 2017 — can help, he said.

“It brings comfort to the families, knowing their relatives’ spirits are not lost, alone, and roaming the earth, suffering,” he said. “Our relatives deserve to be at peace on the lands they thrived on.”

Back in 2015, before anyone knew it could be possible for tribes to retrieve the remains of children buried at Carlisle, about two dozen kids from the Sicangu Youth Council traveled east to Washington. They took part in a White House Tribal Youth Gathering, then drove north to see the site of the Indian school.

To some, Carlisle is best known as the school of Jim Thorpe, perhaps the world’s greatest athlete. To many Native Americans, the name evokes particular menace.

Former cavalry officer Richard Henry Pratt opened Carlisle at an old Army barracks in 1879, the nation’s first federal off-reservation boarding school.

For 40 years, the school worked to “civilize” American Indian children by erasing their names, languages, religions, customs, and family bonds, forcing them to speak English and dress like whites, and teaching them rudimentary job skills. More than 10,000 children passed through Carlisle before it closed in 1918, including about 180 who lie in the cemetery.

White society viewed forced assimilation as a progressive solution to “the Indian problem,” more humane than killing Native Americans outright.

At Carlisle, discipline was severe, and epidemics killed boys and girls weakened by hard labor, bad food, and loneliness. Many boarding-school students around the country saw or were subjected to sexual, physical, or emotional abuse.

Often their suffering was too great to speak of, forever off-limits, even in families.

“That’s something you’re not supposed to ask Grandma,” said Sydney Horse Looking.

She wasn’t scheduled to be on that 2015 trip. But someone canceled at the last moment, and the then-high school senior grabbed her bag and ran to join the others. Always interested in traditional ways, and raised by parents who encouraged her to ask questions, she knew about Carlisle before she arrived at the front gate.

She became upset when stopped for a mandatory security check. Why should she have to prove her identity to be allowed to visit her ancestors? She grew even more emotional upon reaching the graveyard.

“I had a lot of questions in my little 17-year-old mind,” she said. “Put yourself in their shoes: You’re sick, and there’s no treatment. Or you need some comfort, and there’s no one to provide that for you.”

Back home in Rosebud, she and other youths asked the adults on Tribal Council: Why aren’t we doing something to bring the children home?

No one had an answer. But they were willing to act. In January 2016 the council passed a formal resolution to seek the return of the children’s remains, and wrote to the White House and federal authorities.

Today, Horse Looking, 23, is pursuing a degree in early childhood education at Sinte Gleska University in Mission, S.D. She’s also expecting her first child — her pregnancy kept her home from this trip — and finds that impending motherhood makes the fate of the children at Carlisle all the more visceral.

“It stuck in my mind that I would be apart from my family and never come home, and that broke my heart,” she said. “Did they even get to say goodbye?”

The children being repatriated are One That Kills Horse, renamed Alvan, who arrived in the first group of children brought from Rosebud on Oct. 6, 1879. He died less than three years later on March 29, 1882.

Two others among the first arrivals died on the same day 14 months later: Maud and Ernest, whose given name was Knocks Off, the 18-year-old son of Chief White Thunder.

Rose Long Face, or Little Hawk, died in April 1881. Dennis Strikes First died in January 1887. Dora, also known as Her Pipe, was 16 when she got to Carlisle and died about two years later in April 1881.

Lucy Pretty Eagle, also called Take the Tail, arrived at 16 in November 1883 and died four months later. Warren Painter, known as Bear Paints Dirt, died in September 1884, and Friend Hollow Horn Bear in May 1886.

A 10th child who died, Sophia Tetof, has already been returned to her people in Alaska.

“Now the world is seeing what’s happening,” Eagle Bear said. “Sydney said, ‘Why don’t we bring them home?’ We ran with it, and we’ve been running ever since.”