The flames broke out just after 1:40 a.m. in a vacant three-story building near West Genshaw Street and South Kildare Avenue in the city's Lawndale neighborhood, officials said.
The fire spread from that building to a two-story building next door. The four adults and six children who lived in that building all got out safely.
No one was hurt in the blaze. Investigators are looking into how the fire started.