^‘I mean, nothing really happens in your life until you’re 14 or 15. And even then you’re still a child.” Chloë Moretz is thinking back to how she made sense of her character in Let Me In – a centuries-old, pint-sized, preteen vampire. Nothing happens – until you’re 15? That’s not exactly how life as 14-year-old Moretz has lived it. Take Monday night: she was at the Royal Film Performance of Hugo, Martin Scorsese‘s children’s adventure (yes, really). She met Prince Charles, and pictures show her co-star in the film, Asa Butterfield – also 14: Moretz is older by a month – standing beside her, nervy in his stiff, grownup tux. But not Chloë (or Chloë Grace, as she currently prefers to be called). “I was having a giggle with him,” she tells me the next morning in a hotel suite, her voice a few octaves lower than you’d expect. She launches into a friendly, stuttering, somewhat Eeyore-esque impersonation of HRH: “‘I heard you started performing when you were five. Got an old leg up … on the old career … what?'” It’s pretty darn spot-on. “Camilla was very sweet,” she continues. “I had to curtsey and everything. Not a crazy curtsey. It was just a little …” Moretz tips her head daintily to one side.

Moretz must be the most unfazed and unbelievably poised 14-year-old. Ever. And a total pro. She arrived in explosive fashion last year, splattering baddies’ guts and the C-word as miniature assassin Hit Girl in Kick-Ass – or Kick Butt as it’s known in the Moretz household; next came Abby the preteen vampire in Let Me In (a remake of the Swedish film Let the Right One In). She was the best thing in both films, and now has just finished a movie with Tim Burton. “It’s back to Burton’s roots, it’s like Edward Scissorhands and Beetlejuice … fantastical and terrifying, and you laugh at the weirdest stuff. It’s back to what he’s amazing at: straddling that fine line of camp and drama.” Neatly put, especially for someone who wasn’t born when both movies came out. Oh, and Scorsese is like a second dad. He recently called her a “star”, with “powerful charisma” and an “innate sense of emotional honesty”.

Dressed in black with a splash of mustard in her shorts, Moretz is tapping the heels of an amazing pair of suede, high-heeled loafers. Nice shoes. “Thanks, they’re Dolce.” She adds quickly that they are are on loan. “I hope I get to keep them.” For the record: aside from photo shoots and premieres, her mum only lets her wear high-street labels (she loves Topshop and American Apparel).

Moretz seems a bit sensitive about people thinking she’s movie-brattish or spoiled – wisely so, probably. She protests a couple of times that she’s a normal kid. “Everyone around me is so strict about keeping me grounded. My mom won’t let anyone treat me like a little princess.”

And, honestly, she doesn’t come over as brattish at all. But “normal kid”? I don’t think so. She was up till late last night, as her 149,000 Twitter followers will have read at 3am. “Such a great night! In bed now! Night night! Early morning!” The problem is jet lag. “I sat in bed for three hours. It was like 3pm for me.” Now, it’s 10.30 and Moretz can’t have had more than four hours’ sleep. Still, she’s unflaggingly polite, and more focused than any 14-year-old has any right to be. Her conversation is a sweet mix of sophistication and tomboyish exclamations like “wowsers!” Here’s an example: a Tweet she wrote on the flight to London: “Ommgg!!! I get to be in the cockpit with the pilots!!! 🙂 lovin flyin private jets!…” (Her mum, who is upstairs in bed with flu, once confiscated her computer for three months to “detox” her Twitter habit).

But there’s steel there, too. Just how much becomes clear as she explains how she fought for her part in Hugo. The setting is 1930s Paris, but the cast mostly British actors for consistency: Asa Butterfield as Hugo, Ben Kingsley, Sacha Baron Cohen. “I heard that he was only really looking at British girls. When I went in I was like: ‘I’ll do whatever I have to do to be in the this movie.'” At the audition in New York the casting director agreed not to let on to “Marty” that the next actor up was an American. She says she walked in and “tricked” him with a bang-on RP accent. “I think I told him I was from Cambridge.” She gave herself away at the end of the audition, but no matter. Three days later she got the call. “I went up to the balcony in my house and screamed at the top of my lungs: “No way! Oh my gosh! Crazy!”

In the early days, her mum bought her a dog when she got a new part. “She quit that after the third movie.” Moretz pulls a sarky face. Where does all that drive come from? She chews on her gold pendant. “I’m a very competitive girl. In everything I do. When I’ve done gymnastics, ballet or soccer – I was always trying to be the best. I’m really driven. Really driven.”

Nearly contradicting herself, Moretz goes on to say that her character in Hugo, Isabelle, wide-eyed and full-of-wonder, is the closest she has ever played to herself. (“I was able to tune in on my own life”). Among the boxes of movies Scorsese sent her before filming – “he’s like a professor, such a cool guy” – were Funny Face and Roman Holiday. (“Isabelle is a like homage to Audrey Hepburn.”) The last time Scorsese cast a 13-year-old girl, Jodie Foster in Taxi Driver, she had to have psychological testing before signing the contracts. Has Moretz seen Taxi Driver? “No, my mom won’t let me yet. Or Mean Streets.” She knows people compare her to Foster, but she couldn’t possibly comment. “I haven’t been able to see much of her work. That’s the thing.” She says the actor she’d most like to be when she grows up is Natalie Portman.

A lot of people are talking about Scorsese making his first foray into family film: the same is true of Moretz. “I’m legally allowed to go buy a ticket,” she declares, beaming. It doesn’t happen very often. Her first significant film role, aged six, was in The Amityville Horror remake. At 11, She would have been too young to get into both Kick-Ass and Let Me In.

She actually picked up the acting bug as a five-year-old from her big brother, Trevor; he had enrolled at a performing arts high school in New York and Chloë learned his monologues listening outside his bedroom door. Her mum wasn’t keen on the idea of her daughter becoming an actor, but Chloë and Trevor, who is now her acting coach, chipped away. The family are originally from Georgia, and Moretz rolls her eyes when I mention the C-word controversy surround Kick-Ass. “We’re super Southern. If I even uttered a cuss word, I’d be dead. My mom is very strict. It’s not real-life. I’m not going around cussing and killing people and pulling out knives. I’m a normal 14 year-old girl.”

Even so, Moretz is almost scarily hyper-aware of her public image. She’s has that beyond-her-years way of talking that’s inevitable for a kid who spend a lot of time around adults talking business (and let’s face it, multi-million-dollar enterprises hit or miss depending on whether she does or does not nail a role). And yet almost in spite of her protestations, I kind of believe her when she says she’s childlike. She’s off to Winter Wonderland in Hyde Park this afternoon and is beyond excited. (Filming in London for the best part of two years – “we practically live here” – she’s made a lot of friends).

Still, you have to wonder whether the pressure doesn’t get a bit much for 14-year-old shoulders. In another picture taken at the Royal Film Performance, she poses with a man in his late 30s wearing a Kick-Ass T-shirt, who has his arm wrapped around her waist. (Isn’t he old enough to know better?) Moretz is smiling in the photo, but her hands are clenched. Does that stuff freak her out? “No, I love the fanboys,” she answers brightly, on-message. “They’re true fans.” But that guy? “Yeah, I mean …” her voice strains a little, rising noticeably. She gives a “whatever” shug. “I mean you know, that’s why I have my mom, my publicist and brother to protect me.”

Moretz, for better or worse, is one of an elite gang of talented early-teen girl actors working right now: Elle Fanning, the star of Sofia Coppola’s Somewhere, True Grit’s Hailee Steinfeld among them. What’s their secret? They look like good girls who show no sign of going off the rails. Moretz nods sagely: “There’s definitely been a lot of people out there to show us what not to do.” She’s met Fanning a few times: “She just the sweetest girl, like an ethereal forest elf. I don’t know her very well but she’s cool.” As for her own behaviour. “Honestly, I don’t have the room to go crazy, with four brothers and my mom.

“And I don’t want to go crazy. I like being a teenager. I’m not trying to be an older girl, go partying and be all Hollywood.” She says her mum would pull the acting in a nanosecond at the first whiff of craziness. “And that would kill me. It’s the only thing I want to do.”