The fire happened around 8:30 a.m. Friday at a home in the 1500 block of Corlies Street.
The mother of the children, Nina Pitkow, was rushed to Temple University Hospital's burn center.
According to Pitkow's sister-in-law, the boy who was killed was 8-month-old Jeremiah. His 2-year-old brother, Sincere, was in intensive care. 3-year-old Tristan was in critical condition, while 4-year-old Jayla was in stable condition, alert and talking.
Pitkow's two older children, ages 7 and 9, were in school at the time of the fire.
Investigators say the fire started in the first floor front room after the children were playing with a lighter.
Authorities say firefighters arrived three minutes after getting the call, but the house was already fully engulfed in flames.
Witnesses tried to help, but the flames were too intense.
"We heard them screaming and then they just stopped. We tried to get in there but there was no way possible," said Darryl Byrd.
There were six smoke detectors in the house, however the only one not burned out was fully functional and in the basement. It is not yet known if the others were operational before the fire.