Sean Penn on directing daughter Dylan in 'Flag Day': 'I felt I should be calling Child Protective Services'

As a filmmaker, Sean Penn has guided such experienced actors as Jack Nicholson, Viggo Mortensen and Kristen Stewart to memorable performances. For his latest directorial effort, Flag Day, the Oscar-winning actor made the choice to keep it all in the family. Adapted from journalist Jennifer Vogel's 2005 memoir, Flim-Flam Man, the film stars Penn as con artist John Vogel, whose criminal activities sour his relationship with his two estranged children. And to play those children, Penn cast his own kids with ex-wife Robin Wright: Dylan Penn plays Jennifer and Hopper Penn plays Nick, both of whom have to endure the aftershocks of their father's behavior.

"It was really intense," Dylan Penn tells Yahoo Entertainment about performing some of Flag Day's more emotionally fraught scenes with her father either acting opposite her or watching from behind the camera. "I thought it would be really difficult to be that vulnerable and naked, in a sense, in front of 50-something crew members that I didn’t know very well, but I think because I was working with my family, I felt very supported to be able to do that." (Watch our video interview above.)

For his part, Penn sometimes wondered if he'd made a mistake asking his daughter to act out some of the movie's more traumatic moments, including screaming matches, drug abuse and a near-rape by Jennifer's stepfather. "There are a couple of scenes where being the one to have invited her to tear herself apart and being her father were at odds for me," the filmmaker admits. "I felt I should be calling Child Protective Services on myself a few times! But she was so invested and startlingly wonderful, so in terms of being a director dreaming of having a performance to use in a film that way, it was more exciting than depleting."

Rounding out the film's on-screen family unit is Kathryn Winnick, who plays Patty, John's ex-wife and mother to Jennifer and Nick. "What an amazingly talented family," Winnick says of the Penn trio. "Sean and Dylan have such a strong relationship in real life, and that chemistry is so evident when you see it onscreen. Without having such a tight bond in real life, I know it would have taken a lot more — you might not have gotten it if you got two other actors."

Dylan Penn credits both her parents with fostering an open and transparent atmosphere during her childhood, allowing her to avoid the emotional pitfalls Jennifer faced as she grew older. "The movie shows what can happen if you don't [communicate]," she notes. "It can end in real tragedy. You see Jennifer trying to have this transparent relationship with her father and telling her mother that she needs to be protected [from her stepfather]. She’s willing to have an open, honest relationship with her parents and they don’t allow for that to happen. So she finds it elsewhere."

The movie's title refers to John's birthday, June 14 — which is also the date that the Second Continental Congress approved the stars and stripes design of the U.S. flag. (President Woodrow Wilson later designated June 14 as a national Flag Day in 1916 via a presidential proclamation.) Early on in the movie, John's mother warns Patty that she can "never trust a bastard born on Flag Day," as a way to caution her against getting involved with her son.

Perhaps not coincidentally, former president Donald Trump — who Penn has openly criticized as a "failed businessman" — was also born on June 14. Asked whether that piece of dialogue was a sly reference to Trump, the actor declines to explicitly connect the dots. "I think there are a lot of current layers to the movie, and I will leave it to the audience to take it from there," he says, knowingly.

But Penn is certainly willing to share his feelings about what Flag Day means to him, even at a time when deep divisions exist within America. "I think there is a resonance now, because we know the flag of our country has been significantly co-opted by one mindset," he notes. "And in many ways a lot of the rest of us have somehow let it go. What is that bonding symbol of a society that we need and can rely on? I hope it can be a return to some version of our flag that represents the evolution we hope is coming in our future."

Flag Day premieres Aug. 20 in theaters.