The boy was hospitalised following a shooting on Monday at the apartment his mother and two-year-old sister shared with 26-year-old John Hernandez at a public housing project, Ponce city police captain Joel Gonzalez said.
He told The Associated Press the gunmen had chased Mr Hernandez from a drug distribution point in the housing complex and he had fled into the apartment.
The attackers caught him there and opened fire, killing him and injuring the boy, who suffered several bullet wounds.
Captain Gonzalez said police are investigating who placed the foil-wrapped drugs underneath the boy’s clothes.
Gonzalez said a two-year-old girl and two adults who were in the apartment at the time of the shooting were not injured.
He said the children’s mother was not home at the time.
No one has been arrested.