How does the form of "Ballad of Birmingham" heighten its meaning?

In Dudley Randall’s “Ballad of Birmingham,” form and content exist in an ironic relationship. Dudley’s poem uses the childlike qualities of the ballad’s form—particularly its rhyme scheme—to draw attention to the inescapable horrors of racism.
The poem consists of eight quatrains, each with an ABCB rhyme scheme (as is typical of a ballad). This rhyme gives the poem a sing-song, playful quality that reflects the poem’s opening stanza, in which the boy requests to “go downtown / Instead of out to play.” This ABCB rhyme scheme provides the reader with a sense of safety that is not unlike the mother’s own. The rhyme scheme is almost childishly simple, producing a sense of predictability that is revealed to be ironic in the closing moments of the poem in which a bomb goes off in the church.
While the poem does employ an ABCB rhyme scheme, moments before the explosion, there is a minor alteration to this pattern:

The mother smiled to know her child
Was in the sacred place,
But that smile was the last smile
To come upon her face.

“Child” and “smile” produce a slant rhyme—a type of rhyme where sounds are similar but do not produce a true rhyme. It is fitting that this shift in form occurs at the moment when it does. Here, it is the excess of rhyme that marks the impending explosion. Form and content reveal the tragic impossibility of a sacred place or a simple, playful childhood during a historical moment scarred by racism and hate.