Stefan Ringel, a senior adviser to mayor Eric Adams, confirmed the death toll on Sunday, while a city official, who was not authorised to speak publicly, confirmed the number of children dead.
More than 60 people were injured and 13 people were still in critical condition in the hospital, Ringel said.
The majority of victims were suffering from severe smoke inhalation, FDNY Commissioner, Daniel Nigro, said at a press conference.
According to the FDNY, approximately 200 firefighters responded to the scene at the Bronx's Twin Park apartments, a 19-storey building on East 181st Street.
Firefighters "found victims on every floor and were taking them out in cardiac and respiratory arrest," Nigro said. "That is unprecedented in our city."
Nigro compared the severity of the fire to the Happy Land social club fire, which killed 87 people in 1990 when a man set fire to the building after getting into an argument with his former girlfriend and being thrown out of the club.
According to Nigro, Sunday's fire originated in a duplex apartment spanning the second and third floors.
Firefighters found the door to the apartment open, he said, which apparently allowed the fire to accelerate and spread smoke upward quickly.
The fire is not believed to be suspicious in origin but the cause is under investigation.