An unhinged woman menaced a mom and her young daughter with a sex toy and a knife on a Manhattan train before two Housing cops pulling extra crime-fighting duty busted her, law enforcement sources said Friday.

The 42-year-old suspect, identified by sources as Kenya Wescott, started verbally abusing the mother and 11-year-old girl on a crowded D train at Grand Street in Chinatown just before 8:30 a.m. Thursday, sources said.

At one point, Wescott allegedly got in the mother’s face and snarled, “Suck my d–k” before pulling out a dildo and waving it at her.

Wescott then pulled a knife, the sources said.

Two Housing cops who were working extra duty as part of the added subway patrols soon arrested the woman, sources said.

She was charged with menacing, criminal possession of a weapon, harassment and endangering the welfare of a child.

She has seven arrests on her record, including for assault and theft of services, sources said.