Police received a 911 call of a possibly suicidal woman around 2:30 p.m. on Thursday on Long Island.
The caller told the operator that 24-year-old Tenia Campbell was threatening to kill herself and her twin daughters.
Authorities conducted a county-wide search between Medford to Montauk when they found Campbell's vehicle at a Montauk park around 4 p.m., located 60 miles away from their home.
The children, later identified as Jasmine and Jaida Campbell, were inside the vehicle in cardiac arrest and were taken to Stony Brook Southampton Hospital where they were pronounced dead, police said.
Campbell was taken into custody at the scene. She has been charged with two counts of murder.
The circumstances of the toddlers' deaths are not known and the incident remains under investigation.
Neighbors were shocked to hear the news later Thursday evening.
"It was just a typical family, a typical family," neighbor Aleshia Pike said. "The kids were happy, you didn't see any signs of neglect, nothing. They always had smiles, she looked happy."
Both homicide detectives and neighbors are looking for answers.
"Never would have thought she was going through the things she was going through," neighbor Roshonda Campbell said. "She seemed like she had it all together."
Neighbors said Campbell also has a 4-year-old son.
Autopsies will be performed to determine how the toddlers died.