Dawna Langford and her son Trevor
© Courtesy of Kendra Miller
Dawna Langford and her son Trevor were killed in the attack.
The dead included 8-month-old twins, said Kendra Lee Miller, who is related to many of the victims. There were at least eight survivors.

At least nine U.S. citizens, including six children, were killed in a massacre in the Mexican border state of Sonora Monday, a relative to many of the victims told NBC News.

The dead included 8-month-old twins, said the family member, Kendra Lee Miller. Some of the eight survivors, all of whom are children, sustained serious injuries. Miller said a 9-month-old child was shot in the chest and a 4-year-old was shot in the back.

The attack was described by local media as a highway ambush. Willie Jessop, who is related to one victim, told NBC News by phone from Utah that the attack occurred on a motorcade consisting of several families, and that survivors at the scene told him that three cars were shot at and one was set on fire.

"Everyone is in so much shock," Jessop said, adding that he has been in contact with Mexican federal officials and with the FBI. "It's just unbelievable and there's just no way to comprehend it."

The victims were identified by Miller as Christina Marie Langford Johnson, 29, Dawna Langford, 43, and Trevor Langford, 11, and Rogan Langford, two-and-a-half.

Also killed were Rhonita Miller, 30, Howard Miller, 12, Krystal Miller, 10, and 8-month-old twins, Titus and Tiana Miller.

Miller, the relative of the victims, recounted dramatic details from the young survivors. She said Devin Langford, 13, escaped uninjured and then walked for about 14 miles to La Mora for help after hiding his wounded siblings in bushes and covering them with branches.

Ronita Miller twins
© Courtesy of Kendra Miller
Ronita Miller and her twins Titus and Tiana were killed in the attack.
A bullet grazed Mckenzie Langford, 9, in the arm but she also went to find help after Devin did not come back. Miller said Mckenzie got lost and walked for hours in the dark before she was found by search parties.

Miller said Rhonita Miller was on her way to a shopping trip in Arizona with her family and the others were going to Chihuahua to visit family when the attack happened. The victims lived in La Mora, Miller said, which is about 75 miles south of the U.S. border. The community is descended from Mormon settlers, and some members are still practicing members of the church.

There was no immediate indication of who was behind the attack.

El Universal, one of Mexico's largest newspapers, quoted other relatives as saying that members of a Mormon family were killed in what appeared to be an organized crime ambush.