She's a film veteran at 16 and has worked with auteurs like Martin Scorsese and Tim Burton. As she reprises her controversial role as child assassin Hit-Girl in the next Kick-Ass film she tells us, 'I don't want to mess up'

If there's one girl who knows how to deal with C-words, it's Chloë Moretz. She was the child actor who, aged just 11, not only played an ultraviolent pre-teen killer called Hit-Girl in 2010's Kick-Ass, but sent shockwaves rippling through the moralistic media with her casual deployment of the word "cunt". It's difficult to imagine most 11-year-olds uttering the word and living till teatime, let alone having to deal with an onslaught of public scrutiny; the Daily Mail, typically, claimed the film had a "perniciously sexualised view of children", while this paper simply suggested she had brought the word's "noble history" to a close.

"Really? That's so funny!" says Moretz. "I mean, cunt is a funny word. It's a strong word, sure, but more so in America. In England it's just like any other curse word. Anyway, I said it in one take; it wasn't like I was going to go around saying it all over, you know? There's no cursing in my household, but I knew what it meant to make a movie."

The furore has given Moretz, who has starred in no less than 30 films since she was eight, the ammo to take on that other C-word: controversy. There's just as much surrounding Kick-Ass 2: in June, her new co-star Jim Carrey vocally withdrew his support from the sequel due to its "level of violence", a bizarre move, considering that his character, Colonel Stars And Stripes, allows his dog to chew off the nads of an enemy, and that, presumably, he'd not said his lines with earmuffs on.

Moretz, however, accompanied by neither overzealous publicist nor parent, is ready for the question. "I'm not allowed to talk about that," she says firmly, with a beautifully neutral smile and only the merest hint of an eye roll, although she does reject the argument that societal violence can be blamed on cinematic villains. "Like the guy who shot up that movie theatre because of Batman? It's a cop out. But you know... that's Batman. There's been a bunch of different Batman actors. Kick-Ass hasn't got such a long history, so they blame the actors because we're the ones who brought it to life. I think Hit-Girl is the victim. She doesn't know if she's a vigilante or a villain. She never had a childhood."

Chloë's own childhood has been jaw-droppingly busy. Onscreen since the age of six, she's clocked up an impressive range of disturbed supporting roles: a vampire in Let Me In, a werewolf in Dark Shadows, and an unforgettable turn as the scheming heiress who gave Alec Baldwin a run for his money in 30 Rock. In the three years since she swore her way to international notoriety in Kick-Ass, she's worked with some of Hollywood's finest, including Scorsese and Burton, and starred alongside Johnny Depp in last year's Dark Shadows. "Oh my God, I was such an idiot," she says. "He's the coolest guy and he just sort of swaggers in and I didn't know what to say, so I was like, 'I love your necklaces!' and then immediately, inwardly, I was like, 'I am such an idiot, why did I say that?'"

You'd imagine such "I carried a watermelon" moments are few and far between for the Georgia-born Moretz, whose self-possession would be genuinely intimidating if she weren't quite so charming. Her Kick-Ass co-star, Nicolas Cage, called her "marvellously charismatic", and she has a luminosity reminiscent of a young Jodie Foster. Like Foster, Moretz is currently filming a role (in The Equalizer opposite Denzel Washington) that could be considered a classic coming-of-age turn for the prodigious child actress: the teenage prostitute. It's either the next logical step or a depressingly familiar Hollywood move, depending on your point of view. The sudden sexualisation of Moretz on film has the potential to upset a few people.

"When you do a lot of kid movies, that can be a problem. You were a little sister type, and then all of a sudden you're a prostitute, and people don't like it," she muses. "Unless, like Jodie Foster, that's how you start off. And I'm similar because the first time anyone really saw me was in Kick-Ass, killing people. So I don't think I'll have that kind of trouble. I guess maybe we veer towards darker roles because we want to stretch ourselves. I'm a well-rounded girl from a normal family; I'm not a psychopath. So it's fun to be those characters that have all these dark undertones, because it's just acting. Otherwise I'm just playing myself, and I do that every day."

'I do want to push the boundaries, try stupid trends and all that experimental stuff that teenagers do. But I don't want to mess up'

While she will not accept Hit-Girl as a role model, Moretz clearly understands that she herself might be, and rises to the challenge. Any interview with a successful teenage actor comes with a sense of foreboding for their subsequent public decline, but there's not a whiff of it on Moretz, who is as erudite and eloquent as she is breathlessly teenage ("I'm reading The School For Good And Evil. It's about witches. Don't you just love witches?"). She's certain there will be no driving backwards drunk down a motorway, no belligerent Twitter gibberish, no sticky-fingered antics under the influence of pharmaceuticals. "I've never even been to a club," she says, unimpressed by the idea. "I do want to push the boundaries, try stupid trends and all that experimental stuff that teenagers do. But I don't want to mess up." Her career is something she takes very seriously, and she has stringent plans: "I love Natalie Portman. Her whole career from the start till now has been so brilliant and so well-paced. She's always been in control. I think she's perfect in the press."

Unsurprisingly, given her maturity, Moretz says she rarely gets patronised by her co-workers, who in fact tend to regard her as a useful confidante. "I work with a lot of older actors and they all seem to want to talk to me about their marital problems," she says. "And I'm always like, 'Wow, that sucks. I'm sorry!' I mean, my mom and dad got divorced; I've been through a lot at a young age so I'm good at conversing at length about it. It's definitely weird, but I don't find it inappropriate. It's just funny to be discussing it when I haven't ever been in a relationship."

On the other hand, Moretz is wary of growing up too soon, and it's a relief that she turns up for our interview not in an Erdem dress but in a T-shirt inscribed with the words "Boys" in glitter. Like most teens, she fancies a gap year in south-east Asia and she's prolific on Instagram: "God, I know. I kinda just forget I have, like, 500,000 followers! I post all my personal photos but I think they're just for my friends. I'm terrible."

Moretz is currently home-educated, but she was able to relate to the school scenes in Kick-Ass 2, when the seemingly unflappable Hit-Girl is finally shaken by the cliques and mean-girl bullying. She is also fresh from filming a new version of Carrie, the notorious Stephen King novel about teenage angst taken to the ultimate bloody extreme. "Well, I have some experience in that area; I was bullied by my teachers," she says, still indignant. "Can you believe that? This math teacher gave me an F because she said I smiled too much. And I'm great at math! I think they just found it weird that I wanted to act, you know?"

We talk a little about stardom, image and fashion. Moretz has become a style icon, loved as much by her young fans for her look as for her films, and she recently graced the covers of Teen Vogue, In Style, W and Nylon. But it's been clear from the moment we met that this has always been about film, never fame. "Breakfast At Tiffany's was the moment when I really realised why I wanted to be an actor," she recalls. "I saw what Audrey Hepburn does on screen, how when you watch her face she makes you happy, she makes you want to be something." And is that what she wants? "I want to be someone's escape," she says. "And it's silly because it is just a movie, but that's what movies need to be. Instead of getting drunk or doing drugs you can go see a movie for an hour and a half and escape and be someone else and live a different life, if only for a little while."

Kick-Ass 2 is out in the UK on Wed 14 Aug