They were returning from the Mexican state of San Luis Potosi to visit relatives when they were attacked in Tamaulipas, south of Texas.
The 13-year-old was an American citizen and the parents were permanent residents of the U.S., the AP reported.
The highway on which the family was attacked is a high-risk region that is under dispute of multiple drug cartels, according to the AP.
The U.S. State Department has issued warnings not to travel to Tamaulipas state, among other areas of Mexico, due to crime and kidnapping.
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