I get the struggle – Yeats is such a complex poet, right? So, I’d say that the contrast between youth and aging is really central to “Among School Children.” You see it in the way Yeats describes the children with such reverence and almost longing. He seems to be nostalgic for that youthful innocence, especially when he talks about his own body growing older. The line “An old man’s heart is in a child’s heart” shows that despite the aging process, there’s still this connection to youth and what it represents.
About the relationship between the mothers, nuns, and children – that’s where it gets a bit deeper. Yeats seems to be critiquing the roles women are expected to play, particularly in religious institutions. There’s a tension between the nurturing role (motherhood) and the control or discipline the nuns impose. It’s almost as if the poem is asking, can you still retain your innocence or your “true self” when you’re constantly shaped by others?
I’d say focus on the stanzas that talk about the “heavenly” figures, and how Yeats sees them in contrast to the children. That’ll give you a better sense of the way youth and age are linked. Keep digging into the imagery, and I think you’ll uncover more!