PHOTOS: Canadians use shoes to honour 215 children found buried at Kamloops residential school

The remains of 215 children were found at the site of a former residential school for Indigenous children in Kamloops, British Columbia. Some children were as young as 3-years-old.

Prime Minister Justin Trudeau said the discovery is "heartbreaking" and called it "a painful reminder of that dark and shameful chapter of our country's history."

Chief Rosanne Casimir of the Tk’emlups te Secwépemc First Nation called it an "unthinkable loss," and said that while the deaths were talked about, the residential school never documented them.

"We had a knowing in our community that we were able to verify. To our knowledge, these missing children are undocumented deaths," Casimir said. "We sought out a way to confirm that knowing out of deepest respect and love for those lost children and their families, understanding that Tk'emlúps te Secwépemc is the final resting place of these children."

Over 150,000 Indigenous children were required to attend state-funded residential schools as part of a program to assimilate them into Canadian society.

The Kamloops Indian Residential school was one of the largest in Canada and operated from the late 19th century to the late 1970s.

A six-year investigation from 2015 found that school systen, which forcibly separated indigenous children from their families, constituted "cultural genocide."

The report estimated that of all the children who attended these schools, 6,000 died, never returning home.

It also documented horrific physical abuse, rape, malnutrition and other atrocities suffered by many of the children who attended the schools.

First Nations and Indigenous communities across the country have been paying tribute to the children by constructing memorials.