In many of these countries people voluntarily choose to work in these factories. They're terrible places to work, but apparently its still better than working in the fields.
A more effective strategy might be something like: https://www.ijm.org/who-we-are . They work within these countries to protect workers from the worst human rights abuses. (ie child sex trafficking and slavery)
That's a very narrow definition of "voluntary".
Show me people doing things they would do even if they weren't getting paid to do it. That's voluntary.
The presence of compensation does not preclude an action from being voluntary. Neither does the presence of universal biological imperatives like the need for food or shelter. These things are forced on us by nature, not other people, and are part of the basic human condition.
Providing necessary things for yourself is a voluntary action.
Interacting with others of your own free will to provide the things you need more easily than you could do on your own is also a voluntary action.
It only becomes involuntary when that interaction is forced on you, making you worse off than you would have been on your own (as always, from your own subjective point of view).