ABUJA, Nigeria — Armed men broke into a boarding school in northwestern Nigeria early Saturday and seized 15 children as they slept, police told The Associated Press, about 48 hours after nearly 300 students were taken hostage in the conflict-hit region.School abductions are common in Nigeria’s northern region, especially since the 2014 kidnapping of more than 200 schoolgirls by Islamic extremists in Borno state’s Chibok village shocked the world. Armed gangs have since targeted schools for kidnap ransoms, resulting in at least 1,400 abducted since then.The gunmen in the latest…