Any day now, they would have become a family of three. Devoted mom, happy toddler, and a new baby girl so eager to be born that her mother called her "Diva."

Instead, all three perished Friday in a fast-moving overnight house fire in North Philadelphia's Fairhill section.

Firefighters found Elizabeth Perez, 29, near a second-floor bedroom, clutching 2-year-old Nathaniel in her arms. Minutes earlier, she had been outside, counting one, two, three, four, five, six relatives - five of them children - who had made it out safely.

But Nathaniel wasn't there.

Perez ran back inside to save him, but the raging flames and thick smoke trapped them inside.

"She was desperately trying to get out," Fire Commissioner Derrick Sawyer said.

Sawyer said the rowhouse, on the 2800 block of North Fourth Street, had no working smoke detectors. At least five portable space heaters were being used on a night when temperatures dipped to the mid-30s.

Ashley Walker, Perez's cousin, said someone was sleeping downstairs with a blanket near a space heater, and "from there the whole thing engulfed."

Firefighters arrived at 3:45 a.m. and spent more than an hour getting the fire under control.

Sawyer said precious seconds were lost trying to put out the flames. "Because they were trying to fight the fire, it delayed everyone getting out," he said.

A firefighter told Walker, "The whole house burned up in 53 seconds."

Perez and her son lived at the home alone - the same rowhouse where Perez was raised, where her father died of a stroke and her mother died of other illnesses, Walker said.

An aunt and her five children were staying with her when the fire broke out. All six were taken to hospitals for minor issues, fire officials said.

A woman who lived in the rowhouse that shared a wall with Perez's was not home at the time, Executive Chief Clifford Gilliam said. Both houses have been declared unsafe to enter.

Standing outside the charred structure Friday afternoon, relatives and neighbors struggled to make sense of the tragedy.

A cousin, who declined to give his name, crumpled on the sidewalk as he approached.

"She was always helping everybody. Trying to get the kids together, have a block party," he said, wiping away tears. "The way she ran in to save her baby? That's what any mother would do."

The second floor was gutted from front to back, its char looking even blacker next to the first floor's pastel-purple bricks. On the ash-covered steps, small candles flickered alongside a picture of Nuestra Señora de la Caridad del Cobre - the Virgin Mary appearing before sailors on stormy seas.

Nathaniel Jeremiah Richardson "was very ecstatic about becoming a big brother," said Walker, 27.

And the baby, to be named Secret, had seemed unwilling to wait for her Valentine's Day due date. In recent days, Perez's Facebook page was filled with her accounts of several sleepless nights and contractions, and supportive comments from friends.

On Thursday, Walker said, Perez had an ultrasound, and the doctor told her: "Only a couple more days - hang in there."

Walker was to be Secret's godmother, and called her "our baby." They would all be raised together: Secret, Nathaniel, and Walker's own children - a son, a daughter, and a child on the way.

Nelson Santiago, 47, a town watch leader who has known Perez's family for decades, said the neighborhood is tough but tight. Neighbors greet one another in Spanish, as images of Jesus and Mary gaze down from walls and windows.

He described Perez as happy and a great mother, and Nathaniel as a normal boy.

"Last time I remember, Monday or Tuesday, I seen him. He's throwing kisses to my daughter. They were just laughing, laughing," he said.

From his back window, Santiago said, he saw the flames and ran out to help. He helped the six survivors into the ambulance, but for Perez, he said, "it was too late."

"Everybody was screaming and crying. ... I will never forget this day, never," he said, adding that he would pray for Perez's surviving family - three siblings and many cousins. "I know they cannot heal this pain. But I hope they can get stronger."

The deadly blaze came just days after Philadelphia finished 2015 with 12 fire deaths, the lowest total in the city's modern history.

The Fire Department and nonprofits have teamed up in recent years to provide, install, and test smoke alarms in the dense, aging neighborhoods where fires can be most dangerous. They are also required by law.

"Firefighters are out there as we speak, installing smoke detectors on that block," Gilliam said. "Smoke detectors save lives."

jparks@philly.com 610-313-8117 @JS_Parks www.philly.com/MontcoMemo

Staff writer Emily Babay contributed to this article.