Gunmen who abducted a group of children working on a farm in northwest Nigeria’s Katsina state have freed the hostages, the police said. Dozens of gunmen on motorcycles on Sunday last week seized children harvesting crops for a fee on a farm outside Mairuwa village in Faskari district, the police and a local official had told AFP. Officials had earlier reported that 39 children were rounded up by the abductors from a criminal gang who demanded a ransom to free the hostages, but on Sunday reduced that number to 21. Katsina State police spokesman Isah Gambo said late on Saturday that all 21 chil…