SEATTLE -- A 4-year-old boy in a Washington state apartment found a loaded gun under a mattress and used it to shoot his pregnant mother in the face, authorities said Sunday.

The 27-year-old woman and her boyfriend were watching television in bed Saturday when their son found the gun between the mattress and box spring, King County Sheriff's Office spokesman Sgt. Ryan Abbott said.

"He unintentionally shot his mom in the face," Abbott said.

The woman, who is eight months pregnant, was taken to a hospital with life-threatening injuries. She was transferred to another hospital Sunday in improved condition, Abbott said.

The boy's father told deputies he borrowed the gun for protection, Abbott said. The gun wasn't reported stolen and is unregistered, he said.

Under a new state law, gun owners could face criminal charges for not safely storing a gun, but Abbott noted it doesn't go into effect until July.

The case is under investigation.

"We're reminding anybody with a gun, kids see them as toys," Abbott said. "The biggest tragic lesson here is please lock-up your guns so they can't be used accidentally for the wrong reason."