Final answer:
The 'coffins of black' in 'The Chimney Sweeper' suggests hidden suffering and oppression.
Step-by-step explanation:
The phrase 'coffins of black' in line 12 of 'The Chimney Sweeper' from Songs of Innocence suggests hidden suffering and oppression, besides literal death. The use of 'coffins' implies the suppression and confinement of the chimney sweepers, who are forced to endure hazardous working conditions. The color 'black' further emphasizes the bleakness and despair experienced by these children.