"No, baby, no, you may not go, For I fear those guns will fire. But you may go to church instead And sing in the children's choir."
Despite her child's plea, the mother isn't going to budge. She's too afraid that the police will fire on the crowd of marchers. (This gives you a sense of the fear and violence that pervaded life for African Americans in the South during this time.)
Instead, she says that her child can go to church and sing with the other children in the choir. Doesn't get much safer than that, right?