The Metropolitan Police Department said the teen -- who was 16 at the time of the Aug. 28 incident -- was hit with a criminal charge of assault with intent to rob while armed (gun).

The boy's identity was not disclosed.

Cops added they are still on the hunt for an additional suspect ... who they say was captured on surveillance video brandishing a gun at the scene of the crime.

As we reported, Robinson was shot two times -- once in the glute and once in the knee -- after cops say two males attempted to rob him outside of a row of businesses in D.C.

Cops say after the suspects fired on the NFL player ... they fled the scene in a vehicle.

Robinson required surgery to fix the damage caused by the bullets -- but ultimately made a full recovery. He played in his first-ever game on Oct. 9 ... and has logged snaps in every Washington contest since.