Mississauga, Ont. — A six-year-old boy was shot dead by his seven-year-old sister while the two played with a .45-calibre handgun owned by their 22-year-old brother, police said Saturday.

The two young children were playing in a bedroom Friday afternoon when they discovered the high-powered, semi-automatic pistol. The girl pointed the gun at her brother and shot him, police said in a release.

The boy was pronounced dead at Credit Valley Hospital a short time later.

The 22-year-old brother is in custody and faces charges of criminal negligence causing death and various firearms offences. He appeared in court in nearby Brampton, Ont., on Saturday, and was to appear in bail court Monday.

"I can tell you that it's obviously a shocking and traumatic event for the family," defence lawyer Enzo Battigaglia told CBC Newsworld.

Family members accompanied the man to court.

"Investigation suggests the handgun was not registered and its history is currently being examined," Peel Regional Police said in a news release.

The young boy and his sister were under the care of their 18-year-old sister, who was elsewhere in the home, police said. The names of the individuals involved were not released.

"It's tragic for the six-year old that was shot and killed, it's tragic for the seven-year-old that pulled the trigger and it's tragic for the 18-year-old that had the responsibility of looking after the children and obviously it's tragic for the family," Sergeant Frank Mcgonagle of Peel police told CBC Newsworld.

No charges were possible against the seven-year-old, police said. Investigators were working with the Children's Aid Society to decide what would happen to the young girl.

"I am deeply saddened by the tragic death of this child and the trauma this event has visited upon the family," said Noel Catney, Peel Regional Police Chief.

"At the same time, it underscores the danger of firearms and the onus placed on all gun owners to ensure firearms are stored and handled safely."