A home in the upscale Westchester town of Mamaroneck became a scene of carnage Saturday, with cops shooting a knife-wielding 28-year-old woman — and trying in vain to save the life of an injured 2-year-old girl who was also in the house.

Police did not reveal the names or relationship of the woman and child; the child’s death was first reported in lohud.com.

The bloodshed began at 1:30 p.m., when a 911 call led police to the home on Chestnut Avenue, where they found an injured tot, authorities said.

As they tended to the child, the woman began acting erratically, trying to stop them and lunging at them with a knife, police said.

When a Taser failed to stop her, one cop opened fire.

Also rushed to the hospital were four cops — two for wounds sustained in the knife attack and two for evaluation.