They are identified as Elizabeth Perez and her 2-year-old son Nathaniel.
The fire broke out around 4 a.m. on the 2800 block of North 4th Street. Firefighters arrived to find flames shooting from the second floor of the house.
Philadelphia Fire Commissioner Derrick Sawyer says the Elizabeth initially escaped the blaze with other relatives but realized Nathaniel missing. He says she ran inside to save the child.
Officials say the mother and child were found in an upstairs bedroom. Elizabeth had Nathaniel in her hands, but was apparently unable to get back out of the house.
Both were pronounced dead at the scene.
Six people, including four minors, managed to escape and were taken to the hospital in stable condition.
Philadelphia Fire Commissioner Derrick Sawyer said, "It's disturbing that there were at least five portable heaters in the home."
The home had no working smoke detectors, officials said.
So far, there is no word on what sparked the blaze.
The Associated Press contributed to this report.