The two teens were struck early Sunday morning while walking with others along Veterans Memorial near Gears Road.
Both were living at Child Protective Services' offices because the state agency was unable to find a foster home for them.
The death of the 15-year-old is the first time a child has died while living at CPS offices because a foster home was not available.
Investigators said the driver who hit them stopped to help. The driver was questioned, released, and will not face any charges in the accident.
RAW VIDEO: Deputies respond to deadly pedestrian accident
Pedestrian killed by car on Veterans Memorial
Officials say the second foster child, a 17-year-old girl, had run away from two different CPS offices in Harris County since Thursday.
Deputies said there are no sidewalks in the area where the girls were hit.
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