Cambridge-bred do-gooder Ben Affleck took to the Huffington Post and Twitter on Tuesday to continue to spread the word about the death rate of children in the Democratic Republic of Congo. He wrote in his Huffington piece about his work with Secretary of State Hillary Clinton, and why fighting in the North Kivu province of Congo is threatening children. “Families that survive the fighting often face hunger, malnutrition and diseases, which reduce children’s survival prospects and deny them the potential of a promising life,” Affleck writes. Affleck, whose film “Argo” comes out this fall, is in Puerto Rico right now shooting the film “Runner, Runner” with Justin Timberlake. He joined Twitter in June so that he could spread the word about his Eastern Congo Initiative.