A traffic stop of an erratic driver on the Southern State Parkway at about 8:30 p.m. Wednesday in South Hempstead led to the arrest of a West Babylon man for driving while ability impaired by drugs and aggravated driving while intoxicated under Leandra's Law -- after state troopers found two 9-year-old girls in the car.

Police said the driver, identified as William Swinick, 44, was spotted driving his red Kia erratically on the westbound parkway near Exit 20S, Grand Avenue. He told troopers he was trying to drive from West Babylon to Farmingdale to drop off his daughter's friend -- and had become lost.

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Police said Swinick slurred his speech, was "extremely unsteady on his feet" and even used the vehicle "for balance" on "numerous occasions" before failing a sobriety test.

More coverageComplete coverage: Suspected DWI crashes, arrests on LI

The girls were not injured, police said.

Swinick faces arraignment Thursday in First District Court in Hempstead.

Under Leandra's Law, drivers who are intoxicated or impaired by drugs with a child 15 or younger in the vehicle can be charged with a felony. The law is named for 11-year-old Leandra Rosado, who was killed in an October 2009 DWI crash in which the car she was in, driven by the mother of a friend whose sleepover party she was attending, overturned on the Henry Hudson Parkway in Manhattan.

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The driver, Carmen Huertas, was charged with vehicular manslaughter and later sentenced to 4-12 years in prison.