What the family had and prized above anything was their freedom - they had escaped the invading forces, and they would continue to do so for more than 500 days.
During that time, Esther Stermer had to defend her family once, when German SS soldiers raided the first cave.
Coming face-to-face with the men they had lived in fear of for so long, Mrs Stermer held her ground, despite the fact they were pointing guns at her.
Sam Stermer said: 'And she says "What are you afraid of here? The Fuhrer is gonna lose the war because we live here?"'
Saul and Sam Stermer, seen here in the film, say they would not have survived without their determined mother. The soldiers left, never to return, and finally, in April 1944, the Russians liberated the area and the hidden families were able to climb out of the cave into the light.
Last year the Stermer brothers returned to the cave for the first time, for the film. They told how after the war, they travelled to Canada and set up a business, which they still run there.
Today the survivors and offspring of those who hid in the Ukrainian caves number more than 125, and the film, which will be on limited release in the U.S. today and will be released in Germany next month, tells the story of their courage.
Their survival is the longest uninterrupted underground survival in recorded human history