A four-year-old boy in Florida shot and killed his two-year-old cousin with a handgun cops say wasn’t properly secured.

According to reports … officers were called to a home in Kissimmee, Florida on Sunday where they found the two-year-old suffering from a gunshot wound.

The boy — Brayden Tennyson — was taken to the hospital … where he was pronounced dead … just days before what would have been his third birthday.

Osceola County Sheriff Chris Blackmon says the children were alone in a car when the 4-year-old grabbed a gun, which was “literally in the open.” He said adults were standing outside the car when they heard the fatal gunshot.

The family was at a rental house in Kissimmee on vacation from Georgia.