I would suggest that it overlaps. The poem is about the 1963 bombing of the16th street Baptist church in Birmingham, Alabama in which four girls were killed. The church was full of children at this time. The poem however, assumes some knowledge of black history because it is structured as a dialogue between a mother and child, rather than telling the reader details with historical accuracy. It evokes emotions by presenting the singular case out of the multiple cases that made up the dead and wounded that day. This technique perhaps helps the reader to focus on the bond between mother and child, but it nevertheless works better if one is familiar with pictures of information of the bombing. It assumes that one has some knowledge of cultural events and that by reference to these events emotions can be mobilized in the reader that help to keep the memory of the injustice alive.
Primarily because this ballad is a tribute to innocent children, the readers find themselves touched by the poignancy and irony of the poem, rather than the information. Besides, the facts are only sketchy at best. The incident happened in Birmingham, Alabama, and a church on Sixteenth Street was blow up.
The readers must know something about this city as well as the historical context of the poem in order to focus on the information more than on the emotion. And, since the brutal act is committed on a church which traditionally is sanctuary from conflict, and because the victims are innocent of any act that could possibly explain such brutality, the readers cannot but be touched by the poignancy of Dudley Randall's ballad.