PHILADELPHIA (WPVI) -- Three teenagers are under arrest for multiple street robberies and assaults throughout Center City.Police say the trio was behind hold-ups at 18th and Lombard streets, 15th and South and 13th and Spruce.The teens, investigators say, were riding around in a car and then jumping out to rob people on the street.Authorities add the youngsters did not have a gun, and all of the stolen items were recovered.