The fire tore through two units at the apartment complex in the 100 block of East Washington Boulevard.
The units were fully engulfed in flames by the time firefighters arrived.
A 4-year-old boy died in the flames. His 3-year-old brother was critically injured and their mother also had significant injuries. Both of them were brought to a nearby hospital.
The cause of the fire remains under investigation.
City News Service contributed to this report.