Updated at 11 a.m. Tuesday: Revised to include the identity of the fourth victim.

Two men and two children were found dead of carbon monoxide poisoning Sunday morning in east Oak Cliff.

Dallas police and fire officials were called about 9:30 a.m. to a house that is under construction in the 1400 block of Owega Avenue, where the four people were found dead.

A generator powering cellphones and a heater was inside the house, which proved fatal, Dallas Fire-Rescue spokesman Jason Evans said.

Esmeralda Gonzales, the mother of two toddlers, identified them as 19-month-old twins Elijah and Josiah Martinez. She said they died along with their father, Nestor Martinez, who was keeping them for the weekend.

Two workers and two of their children were sleeping in an unfinished house in the 1400 block of Owega Avenue, in Dallas, when they died of carbon monoxide poisoning, officials said. (Rose Baca / Staff Photographer)

Gonzales, 22, said she got a call from Martinez's phone Sunday morning from a detective trying to get in touch with her.

Nestor Martinez poses with his twin sons Elijah and Josiah. They, along with Nestor Martinez's friend and coworker Wilmer Maradiaga, died of carbon monoxide poisoning in an unfinished east Oak Cliff home Sunday morning. (Courtesy of Esmeralda Gonzales)

When officials pulled up to her home in two cars later that day, Gonzales knew right away that something was wrong -- there were no kids in the backseat.

"I already knew. Mom's instinct, you know," she said Monday.

Gonzales said her sons were happy babies who loved to swim and play in the bathtub. Elijah loved to eat, and Josiah often bullied his twin. But the two boys loved each other and hated to be apart.

Gonzales said she is holding her 7-month-old daughter close while she grieves her sons and their father.

"That's the only existence we have left of her dad and her brothers," she said.

Gonzales said Martinez was friends with the other man found dead in the unfinished house Sunday.

The Dallas County medical examiner's office identified him as 32-year-old Wilmer Maradiaga Ordonez.

The two men worked for N.R. Construction, said Hector Medrano, who owns the property and is director and president of the construction company. They'd recently had to move out of their apartments and were looking for affordable options, so Medrano let them sleep in the home for the night, he said.

The men had built other homes for N.R. Construction for about six months but hadn't worked on the house near Glendale Park, Medrano said. Bricks were being installed around the sides of the house, but the front still had blue weatherproof plastic wrapping exposed Sunday morning.

Medrano found the four Sunday morning in a back bedroom of the property near Ledbetter Drive and Lancaster Road.

Dallas Fire-Rescue said the workers usually kept the generator outside and used it after they got finished with work, but they moved it inside after someone had tried to steal it.

"Unfortunately, they did so without realizing the consequences," spokesman Evans said.

The generator was on when first responders arrived, he said. It's unclear how long the generator or the victims were inside, but the generator had been running long enough for the carbon monoxide to reach fatal levels, Evans said.

Neighbors said that the house had been under construction for a few months and that they didn't know anyone had spent the night there while it was unfinished.

Stacey Huffman, 30, who lives a few houses away, said he occasionally saw workers gathered there for cookouts but "not living in there."

Carbon monoxide safety

Carbon monoxide is a colorless, odorless gas that is virtually imperceptible without a carbon monoxide detector. It is produced when fuels such as gasoline, coal and propane burn.

Power generators, which produce carbon monoxide, should be used only in a well-ventilated location outdoors, away from windows, doors or vents. Gas and charcoal grills produce carbon monoxide and also should be used only outside.

Source: Dallas Fire-Rescue