Five young children were killed in a fast-moving fire that swept through a rowhouse on Sunday morning, and fire officials said security bars in the home's windows slowed the attempted rescue.

Two adults escaped but were seriously injured in the blaze. The man and woman jumped from a second-floor window, and the man landed in a wading pool on the sidewalk, officials said.

Officials would not release the names or ages of the victims, but neighbors said the boy and four girls ranged in age from 6 months to 6 years old. Three were siblings and the other two were their cousins, neighbors said.

The adults who escaped were believed to be the parents of the three siblings who died, police said.

The one-alarm fire broke out around 8 a.m. in a two-story stucco rowhouse in the city's Kensington (search) neighborhood and took just nine minutes to extinguish, Fire Commissioner Lloyd Ayers (search) said.

But the attempted rescue of the children was hampered because some of the home's windows were outfitted with security bars, Ayers said.

"The bars usually keep us from getting in and keep residents from getting out," Ayers said. "There were so many things that came together to spell disaster."

It was not known whether the home had smoke detectors.

Firefighters combed through the house Sunday, carting out debris as investigators tried to determine what sparked the fire. Authorities declined to say if there were signs of foul play, but said they would be looking for possible code violations.

Irene Weal, who lives across the street, said the family lived in the home on the block of well-tended brick and stucco houses for a year or two.

She called 911 when she saw the smoke and flames pouring out of the home.

"It could have happened to my kids," she said.

Investigators said they believe the fire started inside the home on the first floor. Four of the children were found on the second floor and the fifth was found on the first floor.

The Philadelphia Medical Examiner's Office (search) said the names of the victims would not be released until Monday at the earliest.

Neighbors said the children were talkative and could often be seen running around the neighborhood and playing in a small pool on the sidewalk in front of the home.

Beatrice Johnston, 73, who has lived on the block in the modest, working-class neighborhood for 20 years, said she was horrified when she saw the house surrounded in black smoke Sunday morning.

"Nobody could get in there," she said.

Holding a picture of the three siblings on her front steps, she said she remembered how they were always polite and energetic.

"They were very friendly and always spoke," she said. "You can't explain tragedy."