(VIDEO) 5-year-old Kentucky boy fatally shoots 2-year-old sister. the 5-year recently received the gun for his birthday.

(CNN) -- A Kentucky mother stepped outside of her home just for a few minutes, but it was long enough for her 5-year-old son to accidentally shoot and kill his 2-year-old sister with the .22-caliber rifle he got for his birthday, state officials said.

The shooting that took the life of Caroline Sparks in southern Kentucky has been ruled an accident, Kentucky State Police Trooper Billy Gregory said.

"It's just one of those nightmares," he said, "a quick thing that happens when you turn your back."

Young children in the area are often introduced to guns at an early age, Gregory said.

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"In this part of the country, it's not uncommon for a 5-year-old to have a gun or for a parent to pass one down to their kid," he said. READ More...