Can you explain the last stanza of the Elizabeth Barrett poem "The Cry of the Children"?

The narrator of this poem is trying to protect young
children from being abused as young workers in industrial England. Her last stanza is a
plea for the government to reform working conditions for the
children:

In
closing, Browning addresses the government saying, " ‘How long, O cruel nation, will you
stand, to move the world, on a child’s heart?" This sentence in the final paragraph of
the poem is the final plea with the country of England to reform the working conditions
of their young and save the lives of the underprivileged
children.

The poem is quite
effective in that Elizabeth Barrett Browing repeats the lines about the children crying.
Children were being exploited. They were used for cheap labor in harsh conditions.
Browning writes about the long hours that children worked in mines and factories. She
mentions that the children do not see sunshine because they are forced to work in coal
mines long before the sun rises until it sets. The cry of the children can be heard as
they gather close to their mothers' breasts. Browning used this poem to point out these
workers were children who needed their mothers.