JOHANNESBURG — Activists say some of the cocoa in your Valentine’s Day chocolate probably came from a West African country where the president is clinging to office. And they note that hundreds of thousands of young children also had a role in producing it. Activists are harnessing Ivory Coast’s political crisis to add momentum to their campaign to force the world’s chocolate makers to improve their labor practices. Some 1.8 million children between 5 and 17 work on cocoa farms in Ivory Coast and Ghana. And opponents of Ivory Coast incumbent leader Laurent Gbagbo say taxes from cocoa go directly to keeping him in power. Still, chocolate makers say they work to promote sustainable livelihoods in West Africa and give back to local communities.