Officers say about 3:10 p.m. on Wednesday, a 16-year-old was walking to his apartment in the Vinings at Christiana when the 13-year-old came out from behind a wall and displayed a knife.
Police say the 13-year-old grabbed the victim and demanded his property. The victim gave the robber his cell phone and the robber fled.
The 13-year-old was found at his home and charged with robbery and other offenses. He is being held at a juvenile detention center.