Jai Farrell died Sunday at a D.C. hospital. His 5-year-old brother, Jordan, passed away Friday.
Firefighters rescued the boys Friday afternoon after responding to a fire at the children's first-floor apartment in Riverdale.
Their father tried to rescue the boys before firefighters arrived. Witnesses said he left the home for a short time and wasn't there when the fire started. He suffered smoke inhalation and lacerations, officials said.
The fire was caused by unattended cooking and was ruled accidental.