A Long Island woman who had been threatening to kill herself and her 2-year-old twin daughters was found hours later Thursday in a Montauk park — parked in the family minivan with the girls in cardiac arrest.

Mom Tenia Campbell, 24, of Medford, has now been charged with murdering the two girls, Jasmine and Jaida, Suffolk police said.

The three were found at just after 4:05 p.m., parked at the entrance of the nature center at Montauk County Park. The girls were taken to Stony Brook Southhampton Hospital, where they were pronounced dead.

Suffolk police did not say how the girls died; there were no obvious signs of trauma to their bodies, law enforcement sources told The Post.

Police had been searching for Campbell and the girls since receiving a call to 911 from the woman’s mother at 2:30 p.m., police said.

“Suffolk County Police Department, assisted by the New York State Police, Suffolk County Park Rangers, Southampton Town Police and the East Hampton Town Police conducted a massive, county wide search for her,” Suffolk police said in a statement.

They searched a 60-mile stretch from Medford east to Montauk, where they found the van by the nature center at 1929 Montauk Highway.

“They had twin Power Wheel Jeeps, and they would always come outside and ride them around while the brother would chase them, laughing and giggling,” recalled Aleshia Pike, who lives across the street from the family.

“They were just your typical little girls — playful happy,” she added with tears in her eyes.

The mother, the twins and an older brother moved into the house in January.

Campbell has been charged with two counts of second-degree murder, police said. She will be arraigned on Friday in East Hampton Town Justice Court.

Additional reporting by Ben Feuerherd and Laura Italiano