How are the ill effects of industrialization explored in the poem "The Chimney Sweeper"?

This poem focuses on the plight of child laborers during the Industrial Revolution. Blake writes in the voice of a child, which lends an immediacy to his words, particularly because the child addresses the reader directly—it is "your chimneys" in which he is forced to work because his father has "sold" him into the service of a chimney sweep.
Blake continually personalizes the children he mentions, which prevents the reader from being able to view them as faceless; Tom Dacre in particular is described in terms which give him a Christ-like aspect, especially in terms of his white hair— suggesting innocence and purity—which curled "like a lamb's back." The other children, in Tom's dream, are also named, but they are in "coffins of black"—a reminder that one of the cruelest effects of industrialization is that many children put to work in this way will die before their time. Orphaned children under an industrialized system are not safe.
Blake draws the strongest attention to this through the use of the poignant dream—the children cannot imagine any means of escape from the drudgery of their lives other than through death. Ultimately, they feel that they cannot be harmed in this world because God is waiting for them, but this is no way for a child to live.

One of the negative effects of industrialization had to do with the way children were put to work doing not only inappropriate but also unsafe jobs. Children, some very young—as the one in this poem was when he was "sold" and could barely cry "'weep!'" (or "sweep")—were thrust into the workforce in order to help support their families, or to relieve families of the burden of caring for and feeding them. This robbed the children of their childhoods, of creating worlds of imagination and fantasy, of playing and learning. They can only dream of "green plain[s]" and "laughing [as] they run." Instead, their jobs could be death sentences, either because they were immediately dangerous or because they affected the children's bodies so negatively, as soot or coal dust will eventually take its toll on the lungs. This is likely why little Tom Dacre dreams that "thousands of sweepers . . . / Were . . . locked up in coffins of black." Only an angel in a dream could release them from their lives of toil and subsequent deaths.