Chloe Grace Moretz can't recall a time when she wasn't in front of a camera. The former child star was 6 when she first appeared in the American television series The Guardian, but even before that, she says, "I've been the star of my brother's [home movies] since I was 2 years old".

Moretz is now 21, and a veteran of major roles in films such as Kick-Ass (2010) and Hugo (2011), and the lead in the 2013 remake of Carrie. She's also had a high-profile on-off relationship with David and Victoria Beckham's son Brooklyn that made her a tabloid target on both sides of the Atlantic.

Moretz grew up in the Deep South, in Cartersville, Georgia, with four elder brothers. Her father, a cosmetic surgeon, walked out on the family when she was 12, reportedly leaving them in serious debt.

From a young age, Moretz says, she was earning for the family.

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"I was like, 'I am a working woman.' I thought I was very adult but looking back on it, I'm like, 'oh my god, I was still a child'. When I was older I had to reconfigure who I was and be, like, don't take things too seriously."

She's taking her new film very seriously.

The Miseducation of Cameron Post is a coming-of-age tale based on the novel by Emily M. Danforth, about an orphaned schoolgirl whose aunt sends her to a Christian gay conversion camp after she is caught having sex with a female classmate. Directed by Desiree Akhavan, it's emotionally involving, sometimes shocking and also very funny.

Even though the film won the Grand Jury prize at this year's Sundance Film Festival, it took months for it to get a distribution deal.

"I think we're the only Sundance winner ... that's taken that long to sell," says Moretz. "But you're talking about a female-led movie, directed by a bisexual American-Iranian woman, and the idea of female pleasure in the movie is something that American buyers and sellers are terrified of."

The film is set in 1993, but as soon as Moretz began researching so-called "conversion therapy" she realised "how insidious it is in America even today".

In the film, the idea of homosexuality as "a choice" and "evil" is propagated by Christian thinking.

"I think it's sad. The Bible is not [inherently negative], but it's ... how people use [it] to manipulate."

Moretz's performance is remarkably subtle for such a young actress. I wonder if she remembers what acting felt like when she was very young.

"I don't know what I do exactly. I've always been an empath and it came very easy to me to just channel these emotions."

Was there a point when she found herself asking, do I really want to do this?

"Yeah, for sure," she says. "I didn't even know acting could be a job until I was about 13, 'cause I saw it as like playtime. But then when I was 19, I had a moment of being like, whoa, I'm 19, I've done 50-something movies, what am I? Who am I? I felt the flame that I'd had my entire life start to dwindle and that terrified me."

She pulled out of the films she was attached to and just stopped. It was, she says, "scary as hell".

"Just to wake up and ... there's no meetings to go to, no script to read ... I realised in that moment that I'd never had quiet."

After 18 months out, she returned to acting last year, shooting the still-unreleased I Love You, Daddy, written and directed by Louis CK. In the film, Moretz plays the 17-year-old daughter of a successful producer (CK), who is seduced by an ageing film director (John Malkovich).

A week before its scheduled release, CK was accused of sexual misconduct and the distributors dropped the film.

"[The cast had believed] that it was a commentary on the industry. [But] after what happened, it took on a very different form", says Moretz.

This isn't the first time that one of Moretz's projects has attracted controversy. Kick-Ass was heavily criticised at the time of its release because of the violence and swearing of its young characters, including Moretz's Hit-Girl. She was left to face the outrage head-on.

"I had to do all the interviews, at 12 years old, and the questions I would get were so crazy. They were like, 'Is your childhood ruined because of this movie?' The truth is, no.

Hit-Girl was one of the most powerful characters I've ever played, and it set me up to not have to prove what kind of woman I am, which is a strong woman.

"People freaked out over that movie, but you look at the characters now for these younger girls," she continues, "and it's become a mainstream idea that a young woman can be a total badass."

I wonder how she's managed to avoid the traps that seem to lie in wait for child stars — the drugs, the alcohol, the wild behaviour.

"I think the traps are there ... it doesn't have to be that you're wrecking a car on Sunset Boulevard," she says. "But there's always gonna be the typical traps of growing up ... and I went through them all, in my own way."

- Telegraph Media Group