A 12-year-old boy was fatally shot in the head while he was sitting in a parked car with two relatives in Brooklyn on Thursday night, police said.

One of the other occupants, a 20-year-old woman, was also shot when gunfire erupted on East 56th Street and Linden Boulevard in East Flatbush just after 7:45 p.m. as the trio were eating inside the vehicle, cops said.

An 8-year-old girl was also inside the sedan and was not injured.

“Once again I’m standing here before you to brief you on another senseless shooting, this time a shooting involving the death of a 12-year-old child,” Assistant Chief Mike Kemper, commanding officer of Brooklyn South, said at a Thursday night press conference from the scene.

It wasn’t immediately clear if the family was targeted.

Two cars, including a black Infiniti sedan, fled the scene after the shooting, sources and witnesses said. One source said investigators are eyeing the possibility that occupants of both vehicles were firing at each other.

The boy, who was seated in the front passenger seat, was struck in the chest and head and transported to Kings County Hospital, where he was pronounced dead, police said.

“I saw the victim in the car, he wasn’t moving,” a witness, who identified herself only as Kinmiko, told The Post.

The 20-year-old woman, who was in the drivers seat, was struck in the right cheek and the upper left leg. She was transported to Kings County hospital and is expected to survive, police said.

The two cars that fled nearly caused a car accident as they sped away, one witness said.

“I heard eight shots and I would say within 20 seconds of the shots, I saw a car on the corner facing East New York Avenue … and they almost got into an accident with oncoming traffic,” one witness at the scene told The Post.

The witness said those who fled appeared to be young.

At least 11 rounds were fired, sources said, and ballistic evidence was recovered from the scene.

Mayor Eric Adams visited the scene Thursday night. During the press conference, he decried the gun violence and vowed to catch those responsible.

“We’re going to catch this shooter. But as long as we have guns and a revolving door system, we’re going to continue to come to crime scenes like this. It’s time for it to stop,” Adams said

Rhonda White, 59, who lives two blocks from where the shooting happened, said she “had a bad feeling that something real had gone down” after she heard gunshots.

“Now I’m hearing that a child has been killed. I have lived in Brooklyn all my life and I thought we were past this sort of thing. But it’s déjà vu. There’s constant fear. The evil has come back to the city,” said White. 

A 45-year-old woman, who would only give her name as Renee, said she was devastated by the boy’s death.

“Every time you hear shots in this neighborhood you hope and pray that this won’t be the one. Well, this time it was the one. I’m in mourning over that poor child. This is what hurts the most, when it’s just a baby who never did anyone any harm. How much more bloodshed before it stops?“