I'm not sure people understand what "unmarked grave" means. Its simply a grave without a marker/headstone and again many people and children were buried in them, cemeteries are full of unmarked graves
An elderly relative of mine in England, long deceased but who I knew when I was a child, had 5 siblings that all died of disease/probably malnourished. They all died young and were buried in unmarked graves. Thousands upon thousands of children in the same city probably were at around the same time too
Many of the childrens` bodies were dumped in shallow graves less than a metre deep straight out of a wheelbarrow. No coffins, no respect, no dignity. Other children were made to watch, some even had to dig the graves, my MIL was one of them. Some of my inlaws too.
Residential school survivors have seen children thrown to their deaths off balconys, die from their injuries after torture, rape and beatings, die in childbirth after forced pregnancies resulting from rape, have the babies from those rapes murdered, commit suicide, die from starvation, die from lack of medical treatment...the list goes on and on.
This was not about kids dying from common historic childhood diseases or conditions, this is not about graves without headstones. And again, this is not just a historic issue, this was going on in the 1990s.