An elderly Queens woman who took in needy foster kids over the years was shot dead when she opened the door to a killer trying to settle a beef with one of her adopted sons, sources said Tuesday.

Leta Webb, 70, was shot in the face and arm when she answered the door of her home on 119th Avenue in South Jamaica at about 1:30 a.m. Tuesday, police said.

“It was definitely a hit. It’s obvious,” said a distraught Eva Usher, 50, the victim’s daughter. “It’s a gang-retaliation thing.

“They didn’t steal anything. They didn’t rob the house,” Usher added. “They wanted somebody dead in that house, no matter who it was.”

Relatives and law-enforcement sources believe that Webb was likely slain by a rival of her incarcerated adopted son, Arnold Webb, a Bloods gang member who has been at war with the Crips since 2009, when he committed a murder.

Arnold is serving 25 years to life behind bars.

Leta’s killer pounded on the front and back doors of the house in the middle of the night, and the mom came rushing from her bedroom.

The second she cracked open the front door, the triggerman shot her.

The gunfire woke up the six others in the home, who found Webb mortally wounded in a blood-soaked entryway.

“Everybody was asleep and then they heard a ‘pow, pow, pow,’ ” Usher said. “They got up and went to the door, and she was lying in a pool of blood.”

Webb was pronounced dead at Jamaica Hospital.

Usher said her trusting mom likely thought the rapping on her door was one of her other children.

Relatives said Webb had lived in the house since immigrating to the United States from her native Belize more than 40 years ago with her now-­deceased husband.

With five biological children, she took in several foster kids through the years — three of whom she legally adopted and raised as her own, family members said.

“I came to her as a foster child when I was 8 months old and she adopted me when I was 5,” said son Benny, 39. “She provided a stable family for me — and now this.”

“She was the only mother I ever knew,” he added. “I feel hurt, bitter, lost . . . Maybe it has not yet completely sunk in.”

Webb’s loved ones described her as a God-fearing woman who treated all kids in the neighborhood like family, and would regularly host summertime barbecues for them.

She would also send money and food to help her relatives back in Belize.

“That was her life,” Usher said. “She was always giving love to her community, and for this to happen to her is unspeakable.”

Additional reporting by Jamie Schram and Natasha Velez