A mother was killed and her two young children — ages 4 and 5 — were left with life-threatening injuries after a vicious hammer attack in Brooklyn on Wednesday afternoon, law enforcement sources told The Post.

Police took a man in custody following the bloody assault in an apartment on 52nd Street near 5th Avenue in Sunset Park at around 2 p.m., according to the sources.

The person of interest, who is believed to have been subletting an apartment in the building, was being questioned by detectives at the 72nd Precinct stationhouse, the sources said.

The mom and her two kids were taken to NYU Langone Hospital Brooklyn, where she was pronounced dead and the two youngsters were fighting for their lives, according to the sources.

The identifies of the victim have not been released.

Police recovered a hammer at the scene.

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