A four-year-old girl in Indiana, United States, was left in a critical condition after her two-year-old brother shot her in the head on Thursday morning (Nov 29).
The incident comes about two years after a four-year-old shot his two-year-old cousin in the US while playing with a gun.
NBC news reported on Saturday that in the latest incident, the children were being watched by their grandparents when the boy shot his sister once in the head.
The young victim was taken to Indiana University Riley Hospital for surgery.
A neighbour, Ms Paula Harvey, told Indiana news outlet WTHR: "This doesn't need to happen. Does not need to happen. Especially to an innocent child."
She added that the children were "very good", and that their grandmother would often take care of them.
Another neighbour, Mr Austin Wise, said: "It's crazy. I see them play. I saw them playing yesterday. I see the father and the mother outside. I talk to both of them.
"How did they get access to (the gun)? Nobody around? Just... it's sad. It's sad."
Local police officer Justin Fuston told WTHR that it was important for gun owners to keep their guns safe at all times.
"A child does not know everything about a firearm and it doesn't take much for an accident to happen... there are (firearm safety) classes all over the place. If you are going to have one, make sure you have somewhere safe to keep it," he said.