-"white man's responsibility" was published in 1899, when the United States just captured the Philippines through the Spanish-American War. These "half demons, half children" are the aborigines of this colony.
The devil means that indigenous beliefs and cultural customs are barbaric.
Children refer to their development in the primary stage of human beings, being naive and needing white education.
This poem was appreciated by President theodore roosevelt, who is famous for his expansionist policies, and was copied and distributed to friends.