The 18-month-old was pronounced dead at Payson Regional Medical Center shortly after the shooting Tuesday afternoon. Police officers responding to calls about a boy who had been shot in the head found the mother in the parking lot of her apartment complex with her son in her arms.
Police Chief Don Engler said the mother had taken her sons to the apartment of a 78-year-old man described as a "family friend." The semi-automatic gun belonged to the neighbor and was not kept in a safe.
Engler said the boys apparently discovered the gun without either their mother or the owner realizing it.
"The children had slipped into another room unobserved by the mother and the 78-year-old occupant of the apartment," Engler said.
The chief said no decision has been made on criminal charges against either adult.
Suzy Tubbs, director of Payson Community Kids, said the mother used to bring her sons across the street to the non-profit. She said the mother liked to "give back" by helping out.
"They were really cute, playing on the playground, playing hard, getting dirty, throwing rocks, typical little boys," Tubbs told KPHO-TV in Phoenix. "This is unbelievable, and our teenagers were saying this is Payson, this doesn't happen in Payson. Well, it happened, and it hit really close to home for them."
Payson is a town of 15,000 in central Arizona about 100 miles northeast of Phoenix.
Celebrity Breakups and divorces of 2014 [PHOTOS]