(CNN) Fernando Batiz says he's "just numb" after the deadly fire that claimed the lives of 12 people in a Bronx apartment building.

A day after New York City's deadliest fire in more than 25 years, Batiz other family members were grappling with shock and grief upon learning an unsupervised toddler started the blaze

Batiz lost his sister, Maria, and her 8-month-old grandson in the Thursday night blaze. He said the baby's mother wasn't home because she was working.

Late Friday, NYPD revealed the identities of several others killed in fire: Shantay Young, 19; Karen Francis, 37; Kylie Francis, 2; and Charmela Francis, 7. Saturday, Mayor Bill de Blasio identified Private Emmanuel Mensah as another victim. The National Guardsman, who was home for the holidays, died trying to rescue his neighbors.

The victims yet to be identified include a 63-year-old woman, four adult men and a male child, the New York Police Department said.

A fatal mistake

A 3-year-old boy's screams alerted his mother that a fire had erupted in their first-floor apartment Thursday night. The boy had been playing with the burners on the kitchen stove -- something he was known to have done before, New York fire officials said.

JUST WATCHED FDNY: Child playing with stove sparked inferno Replay More Videos ... MUST WATCH FDNY: Child playing with stove sparked inferno 03:12

When the mother fled the burning apartment with the boy and his 2-year-old sibling, she made a fatal mistake -- she left the apartment door open.

So each time someone opened a window, more oxygen rushed into the building and fanned the flames.

"Close the door, close the door, close the door," New York City Fire Commissioner Daniel Nigro said. "If there is a fire, you must close the door."

The child and his mother escaped their burning first-floor apartment. But another family on the fifth floor suffered unimaginable tragedy.

Stewart said she lost her daughter, sister and two of her nieces to the flames -- four people from one family.

"I'm brokenhearted to know that a child ... you left the child unattended like that? Come on," she said, tears filling her eyes. "It's a lot."

Her nieces, Kylie and Charmela, were 2 and 7 years old.

The soldier home for Christmas

Emmanuel Mensah

Kwabena Mensah, the father of the 28-year-old National Guardsman who died, said he heard his son was trying to help people get out of the building.

"He brought people outside. He came, went back again, and I think on the third time he couldn't find his way out," he said.

Emmanuel Mensah was stationed in Virginia. His father said he was home for Christmas -- his first trip home since he enlisted a year ago.

Mayor De Blasio spoke about Mensah's heroism in a tweet on Saturday.

Private Emmanuel Mensah was a first generation immigrant, a soldier, and a New Yorker. He gave his life rescuing his neighbors in the Bronx fire. His heroism exemplifies the best of our city. Rest in peace. — Bill de Blasio (@NYCMayor) December 30, 2017

"Private Emmanuel Mensah was a first generation immigrant, a soldier, and a New Yorker. He gave his life rescuing his neighbors in the Bronx fire. His heroism exemplifies the best of our city. Rest in peace."

'People were screaming'

JUST WATCHED Video shows aftermath of NYC blaze Replay More Videos ... MUST WATCH Video shows aftermath of NYC blaze 00:53

The first call to the fire department came in Thursday evening, at 6:51 p.m. ET, the city's fire commissioner said.

"Bunch of calls on this one, chief," an official said over the radio as fire units rushed to the scene. "Baby trapped... apartment 13 is on the third floor. That's where the baby is."

"We've got people on the fire escape," another said.

"The stairway acted like a chimney," the fire commissioner said. "People had very little time to react ... they couldn't get back down the stairs. Those that tried, a few of them perished."

Grappling with loss

Survivors such as Joel Rodriguez now wonder what to do next.

"I'm relieved I'm alive, but at the same time, it's like, where do I go?" the 40-year-old said.

JUST WATCHED Mayor: At least 12 dead from fire Replay More Videos ... MUST WATCH Mayor: At least 12 dead from fire 00:59

The Red Cross is providing temporary housing, along with food, drinks, blankets and mental health care to those residents in need.

Ronn Torossian, who identified himself as a spokesman for the building's landlord, D&A Equities Incorporated, said he was "shocked and saddened at the loss of life and injuries."

"Our prayers and thoughts are with the families that were affected," he said.

So far, officials said they haven't found anything problematic about the building that led to the tragedy.