Going on about downvotes is also against the site guidelines, not only because it's boring (as they point out), but also because it's usually wrong. The GP comment has by now been heavily upvoted. Meanwhile off-topic complaints like this one linger on as uncollected garbage in a thread. Please don't.
Instead of trying to impose additional requirements on buyers, a better approach would be to work at the national governmental level through a combination of carrots (foreign aid and advice) and sticks (sanctions and tariffs for countries that don't meet labor standards).
In this case, it is universally agreed that child slave labor is bad. These lawsuits call for punishing a recipient many transactions away from the mining. It's not calling on the governments, nor the immediate companies involved. Nor is it calling for all parties who are recipients of cobalt, which would include end users. It is just piling onto the two minutes of hate surrounding a couple megacorps.
This is so clearly something that needs to be resolved through legislation and diplomacy. These companies have been purchasing cobalt legally (presumably). If they haven't, a civil lawsuit isn't the answer; criminal charges are.