The shooting happened around 8:00 a.m. Friday at a home in Cresbury Apartments.
The Camden County Prosecutor and Camden County Police said Wednesday that the children did not know the gun was loaded.
The 12-year-old was shot in the face and is still recovering at Cooper University Hospital.
Meanwhile, investigators are still trying to determine how the children got the gun and who it belongs to.
Investigators earlier said a 19-year-old relative of the victim was in the apartment with the boys when the shooting occurred.
Police are working to figure out who owns the gun. There are laws in New Jersey that require gun owners to keep guns safe from children, by either keeping it in a safe place or keeping it locked.