Dirty Old London: the Victorian fight against filth, by Lee Jackson. He blogs at victorianlondon.org.
In nine chapters you discover the various aspects of what made London an unhealthy place in the 19th century as its population grew from 1 to 6.7 million.
The section that most sticks in my mind is from the chapter "The Veil of Soot" on the children apprenticed to master chimney sweeps.
"... most of their apprentices were unwanted and abandoned. Many came from workhouses, and others were - for want of a better term - trafficked by their parents."
"You can buy boys by the dozen. Parents themselves go hawking their children about .."
"In Liverpool, where there are lots of bad women, you can get any quantity you want."These are quoted Jackson takes from the 1874 publication Miscellanies: Stories and Essays, Volume 3 By John Hollingshead.
Put yourself in their shoes, if they had any, and consider why many believe those who got to travel to Canada as home children instead were the lucky ones.