It's extremely unlikely these graves are fake. Why? Because the large number of deaths is not something newly-discovered. It has been known for a hundred years

It's extremely unlikely these graves are fake. Why? Because the large number of deaths is not something newly-discovered. It has been known for a hundred years that large number of children were dying from disease (mainly turburculosis) due to overcrowding. For example Dr. Bryce wrote of the appaling conditions he saw in the 1920s https://archive.org/details/storyofnationalc00brycuoft https://archive.org/details/storyofnationalc00brycuoft One clarification I suppose is that it is unlikely the graves were always unmarked. Most likely they, like many poor people, were buried with wooden crosses which later disintegrated.