CNN —  

The handgun was under a pillow in her grandmother’s Detroit bedroom when the 5-year-old girl came upon it, police said Wednesday.

The girl, who was with two younger children about midnight, was playing with the weapon when it discharged, police said. She was fatally wounded, the latest casualty from shootings by children across the nation.

Her grandmother, who was cooking downstairs at the time of the shooting, was questioned by police and released, said Detroit Police Officer Jennifer Moreno. The investigation into the tragedy continues and no charges have been filed.

The victim, identified by CNN affiliate WXYZ as Mariah Davis, was pronounced dead on arrival at a Detroit hospital.

The other children, ages 1 and 3, were unhurt, police said.

Police Cmdr. Jacqueline Pritchett told the Detroit News that the precinct is working with residents on gun safety. That message is being taken to day care centers and schools.

At least six children have shot and killed either themselves or a parent in the United States since April 20.

The shootings aren’t accidents, according to gun violence prevention activist Jonathan Hutson.

“These fatalities are unintentional, but they’re not accidental,” said Hutson, former spokesman for the Brady Campaign to Prevent Gun Violence. “They’re foreseeable and preventable.”

At least 14 states and the District of Columbia have laws that make gun owners criminally liable if they fail to prevent unauthorized access to guns by children, according to the Law Center to Prevent Gun Violence.

But many children are still shot unintentionally, Hutson said. On average, he said, nine children under age 18 are unintentionally shot in the United States every day. Of those, about seven die each day. Hutson said those numbers have been fairly steady over the past few years.

Twenty-four children under age 4 died from accidental shootings in 2014, the most recent year of data available, according to the Centers for Disease Control and Prevention.

The data don’t distinguish whether those children shot themselves by accident or were shot by someone else.

Hutson said gun owners should keep their firearms locked in safes and store their ammunition separately when children are in the house.

CNN’s Holly Yan and Chuck Johnston contributed to this report.