Saluting the flag at the Whittier Primary School, Hampton, Virginia, circa 1899 – 1900; Frances Benjamin Johnston, 1864-1952, photographer. Click on the image for a larger/higher resolution version of the photograph.
Image Source: Library of Congress, Reproduction Number: LC-USZ62-65770; see here for more details
This picture was taken in 1899 or 1900, just as the full force of segregation was tightening itself around the necks of African Americans – sometimes in a literal way.
Yet, these children – or their parents and teachers – still saw fit to salute the flag. But then, that flag might have freed their parents or grandparents from bondage in the wake of the American Civil War. Some of them might have had family who served in the Union army or navy, or who provided labor to the army at nearby Fort Monroe. So the United States flag was still something to respect and cherish, perhaps even without a sense of irony.
The Whittier School for children was “used as a practice ground for teaching students of the Hampton Normal School” (“Normal Schools” were schools for teachers), which was part of Hampton Institute, in Hampton, Virginia. Hampton Institute was one of many institutions established after the war to provide education and training to the former slaves as they made the transition to free citizens.
Close-up on boy holding the flag
See also A Field Trip to the Freedom Fortress by Hampton Institute Students.
Jubilo! The Emancipation Century 
A very interesting salute?? I would expect hand over heart?
The hand over heart salute was not universal at the time.