The remains of 215 children, some as young as three years old, were found at the site of a former residential school for indigenous children, a discovery Canadian Prime Minister Justin Trudeau described as heartbreaking on Friday.

The children were students at the Kamloops Indian Residential School in British Columbia that closed in 1978, according to the Tk'emlúps te Secwépemc Nation, which said the remains were found with the help of a ground-penetrating radar specialist...