BEIJING; A former doctor armed with a large knife killed eight children and injured five others today at an elementary school in eastern China, a local official said. The assailant was arrested after the 7:20 am attack. He is a former community clinic doctor with a history of mental health problems. Eight children from Nanping City Experimental Elementary School were killed, and five were being treated at a hospital. Six died at the scene. He appears to be in his early 40s.