All six bodies have been recovered from the home and everyone has been accounted for, said fire department spokesman Chief Roman Clark. Earlier Thursday, Clark said the presumed dead were two boys, ages 9 months and 2 years; 3-year-old twin girls; and two girls, ages 10 and 11.
Clark said investigators at the scene had been awaiting recovery of the last body before they begin searching for clues about the fire's cause.
Firefighters encountered heavy flames coming from all three floors of the home when they answered the call about 12:30 a.m. Thursday, and they attacked the blaze from outside, Clark said. The third floor collapsed and the second floor partially collapsed.
The children's mother and two boys, ages 4 and 5, are in critical condition at a hospital. Clark said an 8-year-old girl who helped rescue her younger brothers was in "good shape."
William Malone said all nine are his children with Katie Malone, who's a staff member for Rep. Elijah Cummings' district office.
William Malone told The Associated Press that he was not home at the time of the fire because he was at work for a restaurant. He said one of the three children taken to the hospital after the blaze has since been released.
"I'm still in shock to be honest," said Malone, who was reached by phone at a relative's home. He said he doesn't know what may have caused the fire.
Cummings said Katie Malone has worked as a special assistant in his Catonsville office for nearly 11 years.
"My staff is a family and this unimaginable tragedy is shocking and heartbreaking to us all. I again ask for your prayers," Cummings said in a statement.
Neighbor Robert Spencer said he looked out his window to see the house across the street in flames.
"The flames was coming out on every side, and that's when the mother was coming around the side of the house," Spencer said.
"I heard the kids crying. My daughter heard them. They said: 'Help, help,' and you know, couldn't save them, couldn't save them," he said. "There was just too much fire there."
Michael Johnson, 55, who lives a block away and can see the house from his home, described it as a complete inferno.
"Fire was coming out of every window, and as they sprayed it, it seemed like the fire was fighting back or something. It just kept coming and coming and coming. Fire was actually coming out of the sides of the house. I've never seen anything like that in my life," Johnson said.
Johnson, who didn't know the family, added that he was praying for the people inside.
"It was just so intense," he said. "I didn't think anyone would be able to survive it at all."
WJZ-TV showed two small children sitting up as they were wheeled away on a stretcher and a woman on a stretcher with an oxygen mask over her face. Images from the scene show firefighters dousing the charred shell of the first two stories of the home between two other large three story single-family homes.
Associated Press reporters Sarah Brumfield in Washington and Alanna Durkin Richer contributed to this report from Richmond. Associated Press researcher Rhonda Shafner contributed from New York.