A fast-moving rowhouse fire in southwest Philadelphia early today left four children dead and destroyed eight rowhomes, officials said. The unidentified victims were twin 4-year-old girls, a 4-year-old boy, and a month-old boy, reports Philly.com. All were found in the same rowhome where the fire broke out about 2:45am. The cause is unclear. Officials said more than 40 people were displaced. "This is a tragic, tragic day for the city of Philadelphia. Tragic," says Fire Commissioner Derrick Sawyer. "We lost four children today." (More Philadelphia stories.)