TEGINA, Nigeria—After armed men snatched seven of Abubakar Adam’s 11 children in northwestern Nigeria, he sold his car and a parcel of land and cleaned out his savings to raise a ransom to free them. He sent his 3 million naira ($7,300) into the bush, together with payments from other families in his town of Tegina. The kidnappers took the money, seized one of the men delivering it and sent back a new demand for more cash and six motorbikes. “We are in agony,” the 40-year-old tire repairman told Reuters, still waiting for any sign of what happened to his children three months after the mass abduction. “Honestly I don’t have anything left.” Kidnappers have taken more than 1,000 students since December amid a rash of abductions across the impoverished northwest. Around 300 of the children have still not been returned, according to a Reuters tally of reports. President Muhammadu …