NEW YORK — New York City’s deadliest residential fire in decades apparently began as a child played with a first-floor stove then spread quickly throughout a Bronx apartment building, killing 12 people and leaving four others fighting for their lives, Mayor Bill de Blasio said Friday.

Those who died Thursday night included girls ages 1, 2, and 7, and a boy whose age was not given. De Blasio, a Democrat, says responders saved at least 12 lives.