High schoolers make things awkward that they think should be awkward, but often that's only when the teacher/director shows awkwardness. I would attack the "problem" head on, emphasizing the significance and beauty of the line with an absolutely straight face, confidently as though it was normal. If they think the image of a nursing mother is something other than profoundly beautiful and natural, then they need to be taught the truth!
That said, the Anglican translation may be too much for the undeveloped prefrontal cortex to take in at once.

High schoolers make things awkward that they think should be awkward, but often that's only when the teacher/director shows awkwardness.

I just wanted to thank you for this specifically. There's modesty and decency, but there's also making things awkward when they don't need to be.

Rejoice, Jerusalem, and all who love her.
Be joyful, all who were in mourning;
exult and be satisfied at her consoling breast.

You can see dozens of alternate translations here.
Having looked through them, perhaps the 3rd line might be altered to something like

exult, nurse, and be satisfied; take comfort and be delighted at the abundance of her glory.

* * *

Fr. Weber provides an alternate translation of the whole antiphon:

Rejoice, Jerusalem, and gather with gladness, all you who love her.
Rejoice with gladness, you who were sorrowful,
that you may exult, as blissful as a baby at the breast.