The fire happened last Monday night after flames broke out at a building on Bainbridge Avenue in Fordham.
Liam Parks, 1, was killed and his 6-year-old twin siblings were in critical condition.
On Monday, Eyewitness News learned that the twins, a boy and a girl, have also died from injuries suffered in the fire.
Two adults and three firefighters were also injured in the blaze.
FDNY officials believe that doors left open as occupants fled may have helped the fire spread.
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