The victims were holding a party at their house at the time of the attack, which also left five adults and two children wounded. It was reportedly a birthday party.
The boy’s name was not released, but his nickname — “Little Chapo” — is an apparent reference to imprisoned drug lord Joaquin “El Chapo” Guzman.
The motive in the killings has not been made public, but drug gangs in Mexico frequently dabble in kidnapping and contract killing. They also kill rivals selling drugs on their territory, or people who who them money.
Mexico is no stranger to child killers.
In 2010, soldiers detained a 14-year-old boy nicknamed “El Ponchis” who claimed he was kidnapped at age 11 and forced to work for the Cartel of the South Pacific, a branch of the splintered Beltran Leyva gang. He said he had participated in at least four decapitations.
After his arrest, the boy, who authorities identified only by his first name, Edgar, told reporters that he was drugged and threatened into committing the crimes.
Also Thursday, prosecutors in the northern border state of Sonora said they had arrested a woman linked to as many as nine murders in the border city of Mexicali.
The state prosecutors’ office said that the woman had outstanding warrants for two killings, but that she had been named in seven other homicide investigations. The office did not say what the possible motives might be in those killings.