I'm not defending child labor, but before the West set out on its children's rights crusade ...
This pic stems from 1911. In Pennsylvania, not Congo and not Zimbabwe.
Not sure what the US reaction would have been had someone called for a boycott of Pennsylvania coal back then due to the prevalence of child labor. Also not sure whether the burning of wood for fuel and the further diminishing of US forests would have been the long run better alternative.
And before you all hit me for my - admittedly - relativist views: Yes, child labor is an evil, but also a common stage as a society climbs up the industrialisation ladder - it also ensures the survival of poor families there under the prevailing conditions. The choice there is having the kids go to work so the family has enough to eat as opposed to the children not working and the family starving. If you want to skip that rung, you will have to channel (much) more money into these countries and pay their products/natural resources fair prices plus engage in "nation building" so that the money coming in benefits more than just a corrupt elite. And we all know what a successful concept "nation building" has been in recent times.
The Western World radically and ruthlessly altered its natural environment over many hundreds of years to make it suitable/convenient for our modern industry and services societies as we now move into the digitization era. We had children work in our coal mines so we could get more of that vital modernizing ingredient that is coal cheaper and quicker. And now we tell countries that are 100-200 years (or more) behind us that they should please sacrifice their development for our conscience? And that we know better what is good for them (haven't we always?). That reeks of colonial paternalism to me and if I was from Congo or Zimbabwe I'd be severely offended.