THE Arizona Department of Child Safety says it twice investigated the parents of a nine-year-old boy who was fatally shot in his home.

The agency says it investigated the family after two children were born exposed to a “substance.” The second case was closed in June 2016 after the family successfully completed services.

The parents of Landen Lavarnia, Wendy and Kansas Lavarnia, are facing first- degree murder charges in the boy’s death.

Police say there’s evidence the parents cleaned up the home and waited an undisclosed amount of time before calling police after the shooting. It’s unclear who fired the shot.

It was believed Landen, who died on Tuesday, was shot in the head by his two-year-old brother.

The boys’ mother told police she had previously let the toddler handle the gun when it wasn’t loaded, authorities said.

Landen Lavarnia was declared dead at a hospital in Phoenix, police spokesman Sergeant Vince Lewis said.

Police had initially said the boy died on Monday when he was shot, but they corrected themselves and said he remained on life support earlier Tuesday before dying in the late afternoon.

Ms Lavarnia, 28, told police she had put her loaded gun on a bed within reach of her two-year-old son while she turned to get a holster, according to court records. That’s when the two-year-old grabbed the gun and shot her nine-year-old son, who was playing video games a few feet away, police said.

Ms Lavarnia told police she had allowed “the two-year-old to practise pulling the trigger of this gun when empty on previous occasions,” the records showed.

Lavarnia had appeared in court briefly before the boy was declared dead, and asked the judge whether she could go to the hospital to see him, but the judge said she couldn’t get out of jail without posting a $25,000 bond. The judge also said she had to stay away from victims in the case as well as any children. She didn’t have a lawyer and spoke little during her brief appearance. She was jailed on suspicion of four counts of child abuse — one count for each of her four children in the home.

Lewis says investigators are examining whether to bring additional charges against the boy’s parents.

The father, 31-year-old Kansas Lavarnia, arrived home as police investigated the shooting.

He was arrested because he was barred from having a gun in the family home because of a theft conviction, authorities said. He completed a three-year prison sentence in 2012.

Authorities say he knew there was a gun in his home.

He said only his name and date of birth in his court appearance. He isn’t accused of directly causing harm in the shooting by the two-year-old, said Maricopa County Court Commissioner Paula Williams.

He hasn’t been assigned a lawyer. A review conducted by AAP and the USA TODAY Network found that minors died from accidental shootings at their own hands, or at the hands of other children or adults, at a pace of one every other day during the first six months of 2016.

“It’s gun safety,” Jason Burns, a neighbour of the Lavarnias, told KPHO-KTVK-TV.

“You need to keep it locked up and you need to educate your kids that this is not a toy.

Landen’s school district described him as kind, smart and creative boy who was friends with all.

Washington Elementary School District said in a letter to parents on Wednesday that Landen was enrolled at Sahuaro Elementary School.