The lavish remake by Christian Duguay gets its North American premiere at the Colcoa festival of French Film in Los Angeles on Saturday.
The boys were told they must never let anyone know they were Jews as they went on the run -- by foot, train and ferry -- from Hitler's feared SS secret police in occupied France.
Joffo's 1973 autobiographical novel "A Bag of Marbles" recounted their incredible journey, their capture and subsequent escape, and became a global phenomenon, made into a film and a graphic novel.
Now a lavish remake by Canadian filmmaker Christian Duguay ("Boot Camp," "Joan of Arc") starring French singing and screen legend Patrick Bruel gets its North American premiere at the Colcoa festival of French Film in Los Angeles on Saturday.
Opening in 1941 in occupied Paris, "A Bag of Marbles" introduces cinemagoers to Joseph (Dorian Le Clech) and Maurice (Batyste Fleurial) at age 10 and 12 as they scramble home to the barbershop run by their father, Roman (Bruel).
Roman realizes that the boys' best chance to escape the coming Nazi roundup is to leave the close-knit family and flee to their older brothers in the demilitarized "zone libre" on the French Riviera.
Always just one false move from tragedy, they survive on every scrap of ingenuity and courage they can muster as they try to make their money -- the equivalent of about $815 each -- last and overcome extraordinary odds to elude the Nazis.
"The most important thing is how strong the brothers' relationship was," Bruel, 57, told AFP. "Because they were so strong together, they made it. Because they loved each other, they made it."
Although Jacques Doillon's 1975 version of Joffo's story is regarded as a masterpiece, Duguay and his partners felt the story had enough untapped potential to warrant a remake that would follow the book more faithfully.
Initially unenthusiastic about the prospect of starring in another war movie after 2007's "A Secret," Bruel was persuaded when he learned it would show the Holocaust from children's point of view.
"We must never let people forget what happened, and we have to try to do our best to tell, inform, show, talk, explain," he told AFP.
"Kids are a fantastic way to talk to kids. The identification of the two little boys can resonate in the minds of kids of the same generation."
The film's release comes with the rise of the far right in Europe and the United States, and particularly the success of Front National leader Marine Le Pen in the French presidential election's first round last week, serving as a reminder of the perils of untrammeled populism.
"Ten days before the election, in France we are all very scared of seeing Marine Le Pen being president because it's possible," Bruel said in a Q&A at Colcoa just ahead of his interview with AFP.
"The extreme right goes all over Europe, everywhere. What is happening everywhere is very scary."
Bruel, who has made ten studio albums and more than 50 films, found stepping into Roman Joffo's shoes relatively easy, as his own two boys are the same age as the movie's young stars.
The atmosphere was tense during parts of the filming, which took place just days after Islamists massacred 137 people in cafes, restaurants, a concert hall, kosher supermarket and the Stade de France in Paris.
Bruel's children had been in the stadium just a few days before it was targeted by three suicide bombers from the Islamic State group.
"Emotionally, everybody was very under pressure, so we didn't have to go very far into our deep emotions to be in the situation," Bruel said.
Joffo, now 86, didn't initially intend to publish "A Bag of Marbles," wanting simply to "leave a testimony" to his children and to exorcize his own demons.
A friend persuaded him to send it to publishers and, after more than a dozen rejections, a small publishing house agreed on an initial print run of 30,000 copies. They sold in less than a month and the book went on to sell 20 million copies.
Bruel remembers Joffo breaking down in tears after seeing the movie for the first time, turning to the star saying: "You went further than what an actor can do -- you gave me back my father."
"We had a lot of good times. He's a funny guy. He's a very light person," Bruel said of his meetings with Joffo.
"He came on the set and we had lunch and we talked. He was happy that they cast me to be the father."