Step 1: Highlight the emotional core:
The poem contrasts the vitality of youth (the children) with the fading vigour of old age (the mother), reflecting on the pain of inevitable separation.
Step 2: Final Answer:
The poem centres on the poet's sudden confrontation with her mother's mortality and the quiet grief this brings, softened briefly by images of youthful life, before ending in a poignant, restrained farewell.