The volta, or "turn," in poetry is a rhetorical shift in argument, tone, or emotion, which is frequently signaled by transition words, most notably
"but"... This shift is particularly prevalent in sonnets, where it serves as a crucial hinge point — often marking the transition... or introducing the final couplet.
I don't suppose many children would've thought of this (if it was even intended), either in the studio or at home watching.