| Quote #1
And my father sold me while yet my tongue
The child is the object of the verb "sold," which tells us that his suffering is forced upon him by somebody else. Moreover, he is sold before he can even speak, which implies he's been suffering for a long time, and has no say in the matter.
| Quote #2
There's little Tom Dacre, who cried when his head,
It might not seem like a big deal to have one's hair cut, but it totally is for Tom. The poor kid cries. His outburst shows that even something so simple, like getting a haircut, can represent a form of suffering for a child. It also kind of seems like he's being shaved for slaughter.
| Quote #3
That thousands of sweepers, Dick, Joe, Ned, and Jack,
These poor kids are prisoners—condemned to death—and yet they haven't done anything wrong. How is that fair? And note the passive construction here. The children are "locked up" by somebody else, which reminds us of the beginning of the poem, when the speaker is forced into this work by his own dad. From youth to death, it seems, these kids have no control.