The victims were identified as twin 4-year-old sisters Maria and Marialla Bowah, Patrick Sanyeah, 4, and Taj Jacque, a boy born May 18.
The children along with three others were in the home with the twins' mother, Dewen Bowah, 41, when the fire broke out around 2:40 a.m., police said.
Bowah got the other children, who are her daughters, out, but could not reach the four victims before she was forced to jump from a second floor window, according to police.
Bowah told neighbor Milton Musa the other children were trapped inside but he could not get into the house, police said.
The four victims were found in a second floor front bedroom of the house at 6518 Gesner St. in the Mount Moriah section, officials said. The two boys were the children of Elenor Jacque, 21, who was not at the house when fire broke out.
An initial investigation indicated the fire started in a couch on the porch of the home and spread quickly, authorities said.
Bowah and her surviving daughters suffered non-life threatening injuries making their escape.
The fire displaced about 40 residents of the block, the Red Cross said.
The cause of the fire is under investigation.
"This is a tragic, tragic day for the city of Philadelphia," said recently appointed Fire Commissioner Derrick Sawyer. "We lost four children today."
The blaze was reported about 2:40 a.m. and went to a third alarm before it was declared under control at 4:17 a.m., fire officials said.
The four children were officially pronounced dead at 5:10 a.m., police said.
Jeff Boone, 27, who lives on the block, said he was playing games on his Playstation while his niece slept upstairs when he stepped outside his door and saw a couch on fire on the porch of a house about five doors down.
"As I saw the couch on fire, I ran back in my crib, grabbed my fire extinguisher," he said. But the extinguisher didn't work.
He said the flames spread from porch to porch so quickly "it looked like someone had a flamethrower and just shot it all across."
Boone said he called 911 around 2:40 a.m. then ran around, trying to get people out.
"I was running, screaming, telling everybody, 'Get up! Yo, get yo! Go!'"
He said he ran around corner to the fire station, where the engine was about to leave.
Boone said there was not much he could do after that.
"The flames was just so intense, I couldn't see anything from the smoke," he said. "I heard the little kids upstairs screaming."
Musa, whose house at 6516 Gesner Street was caught in the fire, was awakend by his alarmed roommate.
"'Fire, Fire' he yelled," recalled a shaken Musa. "So I got up and ran out of the house as fast as I could."
Once out of his house, Musa noticed two kids hanging from a neighbor's window, and stopped to help carry them to safety.
"I could see they weren't strong, and I was afraid they'd fall to the cement," Musa said. "So I went underneath them, let them fall on my back and carried them away."
"Everyone was running for their lives," Musa said as he wiped away tears. "I've lost everything. My paperwork, my documents, my house. Everything."
Jaka Kaba's house also was damaged by the fire. But she was more distraught over the deaths of the children.
"I knew them. Everyone knew them. They were good children," said Kaba. "They didn't deserve this. No one expects this. It's hurting everyone."
Battalion Chief Tony Hudgins said that when firefighters arrived four homes were burning and the flames spread quicky to four others.
"It was a tremendous amount of heat and a large volume of fire," he said.
Heat from the blaze melted plastic on parked cars and homes across the street.
"Every time we lose a citizen, it's tough. It's personal, especially when it's a child," Hudgins said. "And it's particularly tough when you don't have a shot to get in there."
About 100 firefighters in 28 fire trucks responded to the blaze.
Sara Smith, a Red Cross spokeswoman, said that as of 8:30 a.m., 28 individuals seeking assistance had checked in at a center the agency set up at Bartram High School.
Written by Philadelphia Inquirer