Devin Blake Langford and his eight siblings were piled into their mom’s Chevy Suburban on Monday, making their way to a family gathering when the domestic tableau was shattered in a hail of gunfire.

Within moments, his mother and two of his brothers were killed by Mexican drug-cartel gunfire right before his eyes.

The horrific scene could have paralyzed even the toughest of adults — but not the steely-nerved 13-year-old, who ushered his six surviving siblings into a hiding spot before bravely trekking 14 miles through war-torn cartel turf to seek help, according to his family.

Mom Dawna Langford was driving the clan from their community of LaMora in Sonora, Mexico, to visit family — when all hell broke loose.

“All of a sudden, bullets just rained from above, from on top of a hill, down on top of them,” relative Lafe Langford told CNN on Wednesday.

Dawna, 11-year-old Trevor and 2-year-old Rogan were all slain.

Once the firing stopped, a group of men came down from the mountain and “pulled all these kids that were still alive,” Lafe Langford said, recalling what the survivors told him had occurred.

“They basically told them to get out of here. So they immediately started walking toward home.”

It was unclear whether those men were the same who opened fire.

“After witnessing his mother and brothers being shot dead, Devin hid his six surviving siblings in the bushes and covered them with branches to keep them safe while he went for help,” relative Kendra Lee Miller posted to Facebook.

Dawna Langford’s vehicle and the two other SUVs in the convoy were ambushed by La Línea, an armed wing of the Juárez cartel, that mistook the group for a rival faction of the Sinaloa cartel — once run by ruthless kingpin Joaquín “El Chapo” Guzman — known as “Los Salazar,” Mexican army chief of staff Gen. Homero Mendoza said at a press conference Wednesday.

The ruthless thugs may have confused the group’s large SUVs for those the Salazar gang, who have been linked to the vicious crime ring.

“We can determine that this was not a direct attack [against the families],” Mendoza said, ­according to local news outlets.

“The types of vehicles [the families] used are common in that mountainous region and are used by organized-crime elements,” he added.

Authorities deduced that the families were not intended targets since “those who attacked the occupants [of the vehicles], they let the children go.”

But hours after the children were spared, as nightfall loomed and Devin hadn’t returned, his 9-year-old sister, McKenzie — who had been shot in the wrist — grew worried and said, “I gotta find him,” according to Lafe.

“She had a bullet through her wrist, but nevertheless she was probably in the best shape to walk at that point. And so away she went,” Lafe said.

At about 5:30 p.m., Devin got back to LaMora, bringing with him news of the massacre that also left two other mothers and four other children — including 8-month-old twins — dead.

“Devin’s uncles armed themselves with guns and returned to try and find the hidden children, knowing many of them were injured,” Miller wrote.

The relatives, aided by Mexican soldiers, first found McKenzie at about 9:30 p.m. “We found her by her little footprints,” Lafe said. “She took the wrong road . . . and we saw that her footprints had a shoe, and then a bare little foot because she had to take her shoes off, and her feet were just swollen and covered in blisters when they found her.

“The first thing out of her mouth was: ‘We have to go back. We have to go back. My siblings, my brothers and sisters are dying. They’re bleeding, they’re shot. We have to go rescue them.’ And that’s all she cared about,” Lafe said.

Five siblings, who were injured, were taken to a local hospital until their father, David Langford, arrived from Tucson, Ariz., and accompanied them in a helicopter to be treated at a US hospital back in Arizona.

Devin, his brother Jake and 7-month-old Faith Marie Johnson — who was found in a car seat that her slain mom Christina Marie Langford Johnson put on the floor in a heroic act to protect Faith — remained in the care of their aunts and grandmothers in LaMora.

“What they went through, what they experienced — we don’t have the capacity just to imagine what these children went through,” Lafe said.

The doomed group, who had dual US-Mexican citizenship, appeared to be part of a remote farming community, sources said. They call themselves Mormon but are not affiliated with the church.

They are descendants of former members of the Church of Jesus Christ of Latter-day Saints, who fled the US to escape the church’s 19th-century polygamy ban and have had past run-ins with the cartel.

Drug traffickers once kidnapped a 16-year-old member of the clan who was released after the family refused to pay a ransom. The teen’s 31-year-old, brother Benjamin LeBaron, was killed by cartel goons in 2009.

The family believes the drug targeted them.

“Three vehicles with women and children in broad daylight. There was no mistaken identity,” Taylor Langford, a nephew of one of the women killed in the attack, told CBS News Tuesday. “I felt this was in broad daylight and . . . no one could have done that not knowing what they were doing.”