Step 1: Poet and poem.
The poem is written by Kamala Das, known for her confessional poetry.
Step 2: Central theme.
While traveling with her mother, the poet notices her mother's pale, aging face, which reminds her of death and separation.
Step 3: Contrast.
She contrasts her mother's frailty with the energy of young children playing outside.
Step 4: Conclusion.
The central idea is the poet's deep emotional bond with her mother and her fear of inevitable loss.
Final Answer: \[ \boxed{\text{The poem conveys love, aging, and the fear of separation.}} \]