OUAGADOUGOU—A massacre in northeast Burkina Faso in which more than 130 people were killed this month was carried out mostly by children between the ages of 12 and 14, the government said. Armed assailants raided the village of Solhan on the evening of June 4, opened fire on residents, and burned homes. It was the worst attack in years in an area plagued by jihadists linked to ISIS terrorist group and al Qaeda. Government spokesman Ousseni Tamboura said the majority of the attackers were children, prompting condemnation from the UN. “We strongly condemn the recruitment of children and adolescents by non-state armed groups. This is a grave violation of their fundamental rights,” the UN children’s agency UNICEF said in a statement on Thursday. Despite interventions from UN peacekeepers and international armed forces, attacks by Islamist extremists continue unabated across West Africa’s Sahel region, including neighboring Mali and Niger. Local officials …