The incident happened at Fallbrook at the north Beltway on the westbound feeder around 11:30 p.m.
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The girls were being driven by their father Luis Aguilar, who police said showed signs of being heavily intoxicated.
Deputies said the 31-year-old drove directly into the traffic light pole, and neither child was properly restrained in the back seat.
The 4-year-old was wearing an adult seat belt while the 5-year-old didn't have anything protecting her.
"If you have the responsibility of children, they don't have a voice, they can't say 'Dad don't drive', they can't say 'I need to be on booster', they rely on you," said Sean Teare, with the district attorney's office.
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Aguilar has been charged with murder along with intoxicated assault involving a vehicle.
This is the second crash involving a DWI in less than 24 hours that has killed a minor.
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