The reader may well know that Birmingham, Alabama, was a hotbed of racial tension and the 16th Street Baptist Church was an organizational setting for major players in the movement for racial equality.
The anonymous mother, who represents the six mothers who lost their children in the bombing, must not have realized that the 16th Street Baptist Church in Birmingham was the site of many meetings of the Southern Christian Leadership Council whose local organizer was the pastor in residence, Reverend Fred Shuttlesworth [the Birmingham airport is now named after him]; in addition, James Bevel, SCLC leader who began the Children's Crusade, teaching youth about non-violence, as well as Dr. Martin Luther King, Jr. were regular speakers at this church. The bombing took place at this church because these men were often present, and the church was viewed as a center for racial protest.
Rather than allowing her child to go into the streets and partake in a racial freedom demonstration, which could, indeed, become dangerous, the mother, ironically, sends her daughter to the church where she believes her girl will be safe. This is an example of dramatic irony since there is a contradiction between what the mother believes (that her girl will be safe) and what the reader knows to be true (the church is not safe).