Viggo Mortensen on new movie, "Captain Fantastic"

Viggo Mortensen is best known for his role as Prince Aragorn in "The Lord of the Rings" trilogy. But in a very different gig in his new movie, "Captain Fantastic," he plays a father of six children - ages seven to 18 -- raising his kids off the grid in the Pacific Northwest.

"The script and the movie -- as an actor I was inspired and it's one of the best movies I've been in, but as a father, very intimidating," Mortensen said on "CBS This Morning" Tuesday.

Mortensen plays Ben Cash, who wants to keep his children away from the influences of modern society. But following a family tragedy, they are forced to face the outside world.

"As a story, it's a very well-made family drama. It's moving, it's funny, it's thought provoking, but I also felt... that it touches on the roots of the social discord and polarization in society," Mortensen said. "Because it's a movie story that speaks to the importance of self-reflection, being willing to make adjustments... honest communication and finding a new balance with people who think differently than you do."

Perhaps the movie is too honest at times. That's because of Ben Cash's unconventional parenting style -- having frank, blunt conversations about taboo subjects with his children, such as sex and death.

"As radical as this family seems, the foundation of the family model is complete honesty, constant curiosity and open discourse. Sometimes it's brutal. Sometimes you go, 'God, I can't believe you said that to a seven-year-old," Mortensen said.

But in order to portray that, a strong cast of six children - who Mortensen described as "genius" -- was critical. In fact, in order to prepare for their roles, the cast went through a grueling two-week boot camp that included everything from taxidermy lessons to rock climbing to martial arts training and more.

"The kids have to convince you - even if they're seven years old - that they can handle that language, that they really know what you're talking about... complicated ideas, scientific terms, philosophy," Mortensen said. "I mean, there's lot of scenes in the movie that are very funny because you're just stunned that a little kid can master that kind of conversation."

"Captain Fantastic" is playing in theaters now.