A buyer would have to become more engaged with the companies they are purchasing from. Establish minimum standards, Conduct routine audits. May have to place FTE in country to continuously monitor compliance and provide assistance. Would have to probably pay more for products from companies willing to commit to these regulations.

David Cottrell, although the material extricated is used in the manufacturing of some of our societies most powerful personal devices, the tools used to cultivate the cobalt are primitive, the conditions abysmal as you are aware.
Shoeless, gloveless, and with no protection from the residual dust or elements of nature, the children work for upwards of 12 hours a day. So, first we need to make sure that authorities note of inhuman way of using children and Adults. What people are doing is just making sure they get the meat but how it is done they don't care. So, Government and Authorities need to wake up.

The "customers" need to be more diligent and put more effort into ensuring the product they're buying meets their standard for safety and decency.
Similar to fair trade coffee, cobalt needs to go through a similar industrial upgrade.
Here's one company making steps in that direction - https://www.reuters.com/article/metals-lmeweek-trafig/lmeweek-trafigura-to-invest-in-congo-artisanal-cobalt-mine-idUSL8N1WM0FN

Diamonds have a similar problem. In a sense they have the same problem but even more so as no one needs a diamond. From my understanding the move to eliminate 'blood diamonds' has had limited success. Certificates of ethical mining etc can be faked, supply sources muddied, paper work on 'good diamonds' can be duplicated and used for others. The effectiveness of these measures, or ineffectiveness, should be used to evaluate any proposed measures for critical technology elements. It would also be interesting to see if block chain could be useful here, anti forgery measures are listed as one of block chains greatest strengths. All of these solutions preface a stable and coherent political system at the mining site.

It is a sad truth about human nature that is reflected in these practices. Valuable minerals draw competition and very rapidly unethical behavior. When a mineral with global demand and limited availability is discovered in abundance in a tragically poor area the results are compounded and negatively for all but the wealthiest investor and government officials. DRC is a loosely organized government with rampant corruption. For commentators that have mentioned informing authorities... consider that the authorities own and fiercely defend the unregulated mines, they will do nothing. Just as the blood diamond trade rapidly adopted "ethical certification" for mines that routinely change ownership by strawman companies simply to avoid revocation of the certificate or public awareness of loss. No real results and a highly profitable side market for fake certificates.
It will very likely take the evolution of the local government to make any strides. The BUY side of the transaction just has too many outlets that don't care. If the US and EU stopped buying Cobalt from DRC due to ethical mining concerns China, Russia, India would buy up the supply and sell it to US and EU for a markup. Resulting in higher cost devices and consumers are already sensitive to price. Global policy relating to child labor is a meritorious goal but one that requires a universally accepted age for employ.
There are no easy answers and while I agree that some pressure can come from buyers and consumers I know for certain US consumers don't care about the source as long as the price is low. Even with paper certificates of ethical mining the market is too competitive for such a program to have any affect. This issue certainly needs more thought, more ideas and international involvement. It bothers me as a human that there are places like this that consider it normal for their children to waste away in a dangerous mine at 9 years old just so they can eat regularly. I would love to be part of the solution.