According to investigators, the boy apparently found an unsecured 9 mm pistol inside a bedroom.
"It appears the 6-year-old got up and went into a room and found a firearm and discharged it," said HPD Homicide Sgt. Anthony Turner.
The child's mother was not at home at the time, but her 18-year-old daughter was looking after the children this morning. In addition to the victim, they include his 6-year-old twin sister and a 14-year-old sibling.
The boy was taken to a hospital where he was pronounced dead.
His 20-year-old sister told police that she had the gun because of crime in the area.
"She said there had been burglaries and she had the gun for protection," Turner said. "We're still in the early stages of the investigation about where the gun was located but it appears it was accessible to the child."
It's the second death in as many days of a child who played with an unsecured weapon.
On Saturday, a 4-year-old Texas City boy was killed when he found a loaded handgun at his family's home.
Police also say that should be a tragic reminder that weapons should be locked in safes and out of children's reach.
Complacency, Turner said, is another danger.
"Maybe you put it in a drawer or somewhere else you don't think the kids are going to go through. Unfortunately, they find it and you wind up with situations such as this."
ORIGINAL REPORT: Boy dies after accidental shooting in NW Houston
Boy dies after accidental shooting in north Houston
Reporter Deborah Wrigley reports from the scene
6-year-old boy accidentally shoots himself to death