Prime Minister Justin Trudeau say di tori na "painful reminder" of di "shameful chapter of our kontri history".
Di central government take over administration of di school for 1969, and e operate as residence for local students until 1978, when dem close am down.
The children were students at the Kamloops Indian Residential School in British Columbia that closed in 1978, according to the Tk'emlúps te Secwepemc Nation, which said the remains were found with the help of a ground penetrating radar specialist.
Manny Jules, who was chief of the Tk'emlups for 16 years, said he wants an apology from the Catholic Church for its role in operating residential schools across the country.
"The loss of 215 children found on the grounds of a residential school is a national tragedy", Chief Bobby Cameron of the Federation of Sovereign Indian Nations in Saskatchewan said in a statement.
Rosanne Casimir, the chief of the community in British Columbia's city of Kamloops, said the preliminary finding represented an unthinkable loss that was never documented by the school's administrators.
What do we know about the remains?
Casimir said what the nation called "the knowing" about the missing children fuelled the search. She add join say, "some di bodi na of pikin wey dey as young as three years old".
The Union of B.C. Indian Chiefs said Friday was a day to honour the lives of those children, and hope for peace for their families.
Survivors started calling her Thursday when the discovery was made public, saying they can't sleep because the reports triggered frightful childhood memories, she said.
The reaction has been one of shock, grief and contrition.
"And perhaps repatriation to their respective communities because the students come from not only the Tk'emlups te Secwepemc area but also neighbouring communities and as far north as Fort Nelson", he said.
"The news that remains were found at the former Kamloops residential school breaks my heart", Mr Trudeau wrote in a tweet.
Indigenous communities throughout Canada, ChiefCasimir said, had children who were forced into residential schools only to vanish. Di goment dey committed to "memorialising di innocent souls wey die", she tok.
They are working with the community and partners such as the BC First Nations Health Authority, to provide resources and the support needed as determined by the community, the ministers said.
"That this situation exists is sadly not a surprise and illustrates the damaging and lasting impacts that the residential school system continues to have on First Nations people, their families and communities, " its CEO Richard Jock wrote in a statement.
The Truth and Reconciliation Commission concluded in 2015 that residential schools were a program of "cultural genocide". To date, more than 4,100 children who died while attending a residential school have been identified, it says.
"These were children - all belonging to a family and community, and a nation - who were forcibly stolen from their homes under the authority of the Canadian government, and never returned".
"I think it speaks to those stories of those children who said, 'There were always stories of these burials, and whatever happened to this kid who went missing in a supposedly random way,"' he said.