Updated at 9:40 p.m.: Revised to include additional information from police.

A child was shot in the head Sunday evening in Arlington by his brother, police say.

The 6-year-old boy was shot about 4 p.m. in the 1400 block of Cloyne Drive, near Mansfield Webb Road, police said.

A group of children were playing in a room when the boy's 10 or 11-year-old brother found a rifle, pointed it at the child and pulled the trigger, Lt. Christopher Cook said. It was not clear whether the shooting was an accident.

The wounded child was taken to Methodist Mansfield Medical Center, but was later flown to Cook Children's Medical Center. He was in grave condition Sunday night, police said.

Another child, the boy's 6 or 7-year-old sister, was struck with shrapnel, and is expected to be OK, Cook said.

An older teen in the home told police that the .22-caliber rifle was his and that he had purchased it. Cook said the parents told officers that they did not know that there was a firearm in the home.

Police will conduct a criminal investigation to determine where the gun came from and how the children were were able to access it.

The child was one of three who were shot Sunday in Tarrant County. An 8-year-old girl was wounded in Arlington in what police were investigating as an accident, and in Fort Worth a 4-year-old boy died after being shot by his sibling.