The point was not that it's ok for the mines, the point was that there is nothing unique about them, and there isn't much justification for focussing on them. Not to shield them from scrutiny, but to avoid making them into a distraction from child labor and slavery in general.
If you drummed up a big movement to deal with the problem of child slave labor in lithium or cobalt mines, what good have you done for the world or the kids? The same kids are still at the same risk tomorrow as they were yesterday, they just wind up in some other kind of operation, or in the extreme case maybe their only value (to those people) becomes as organ cattle. Great job!
It's a distraction to pick a specific example like that and present it as some kind of unique problem. What specific work they are put to is not the problem, it's the fact that they are enslaved at all.
It's also to say that "the green revolution is fueld by trafficked child labor" is a mischaracterization, because it is not fuelled by child labor, it merely includes child labor.
The cotton industry in the US was fuelled by slaves, because the labor was 99% done by slaves, not merely that there were some slaves.
The green revolution is such a large thing that 40k children are hardly a drop in it.