(By Michael Biesecker, michael.biesecker@newsobserver.com) A private mental treatment center for children in Charlotte could be shut down after a series of violent incidents, including the staff hitting patients and a teenager stabbing another child in the eye with a rusty nail.State inspectors who toured The Keys of Carolina in September and February found multiple violations that "endanger the health, safety and welfare" of the children, who range in age from 12 to 17.