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Melissa DeLoatch was standing with her six children outside a 7-Eleven in Garnerville, N.Y., on Wednesday afternoon when her husband, Sean, asked a man who was smoking nearby to move away from the children.

He and the man, Jason Mendez, began to argue, the police said.

Then the unthinkable happened: Mr. Mendez got into his car and drove it into the family, the police said. He reversed 20 feet, the police said, shifted back into drive and plowed into the family a second time.

Ms. DeLoatch, 32, who family members said was pregnant, was killed. She put herself between the car and some of her children as she pushed the others out of the way, her brother said.

Her husband and their six children, who ranged in age from 10 months to 10 years old, were injured but are all expected to survive, the police said.