The devastated mom of the little girl killed when a granite railing toppled on her outside a Brooklyn home told The Post through tears Friday that the tragic incident happened in the blink of an eye.

“It took a second,” a crying Maria Lorensa Chaumana Camacho said in Spanish of the freak incident that left her only child, 5-year-old Alysson Pinto-Chaumana, dead.

“We were just walking, and she was playing,” the mother said. “She was playing with the wall. I looked to the street for a second. She touched it, and it fell on top of her.”

The little girl was in the front yard of a relative’s home at 444 Harman St. in Bushwick with her mom around 9 p.m. Thursday when a 6-foot-long, 3-foot-high granite railing — which likely weighed between 400 and 500 pounds, according to a construction expert — crashed down on her.

“It’s very painful for us. Very painful,” said the mother, a native of Ecuador who’s been living in the US for the past seven years.

She called her daughter “a very happy child, very intelligent. She loved to play.”

The mother and daughter were at the three-family residence visiting a relative, the homeowner said.

Surveillance footage obtained by The Post shows the child walk up to the heavy fence while inside the gated front area of the home moments before it suddenly falls on top of her.

The child suffered head trauma and was rushed to Wyckoff Heights Medical Center, where she was pronounced dead.

Additional reporting by Georgett Roberts