You can’t accuse Chloe Moretz of copying the performance of young Swedish actress Lina Leandersson in “Let Me In,” the Hollywood remake of “Let the Right One In.”

“I was too young to see ‘Let the Right One In.’ I wasn’t allowed. It’s R-rated.”

And Moretz, a screen veteran, playing a vampire in “Let Me In” — also the once and future Hit Girl of “Kick-Ass” — can only act in R-rated movies. She can’t see them in theaters. She’s 13.

“As you can imagine, my family has a lot of boundaries about what they’ll let somebody my age, a young girl, do on film,” she says from the set of Martin Scorsese’s 1930s fantasy, “Hugo Cabret.” “Everybody says ‘You’ll be more mature, working around adults all day, being in the business.’ But I’m still a little girl. I’m still just Chloe.”

But “just Chloe” is already an actress making her mark, and not in conventional child actress roles. We first noticed her as the smart tween sister of Joseph Gordon-Levitt’s lovesick romantic in “(500) Days of Summer.” She was wise beyond her years, even in “Diary of a Wimpy Kid,” a middle schooler who proves girls emotionally mature faster than boys.

In this, her breakout year, Moretz did able support in “Wimpy Kid,” then flat-out stole “Kick-Ass,” the comic book adaptation about a teen who becomes an inept costumed crimefighter, only to meet a tween (Moretz) whose dad (Nicolas Cage) raised her to be a competent one — Hit Girl.

“I’d always wanted to do an action film, and that was so awesome,” she says, taking some pains to avoid saying the title out loud. “How many young girls get to do the stuff I got to do in that one? Guns and knives and fights and all.” She’s already on board for a sequel to that one.

And “Let Me In,” in which she stars as a 300-year-old vampire who never aged past 12 and who reluctantly befriends a boy her age, is earning her the best reviews of her young career. The Hollywood Reporter noted that she has “the soulful depth and pre-adolescent vulnerability necessary to keep it compellingly real.”

Like seemingly every other girl her age, she is all about vampires. “‘Interview With the Vampire’ is my favorite. I love how crazy and fake they all are. I mean, they can’t be real, right? It so can’t happen. And when it can’t be real, you can do all these interesting things with the characters.”

For instance, she and director Matt Reeves talked over “how hard it is for an older person to remember things even from their 20s when they’re in their 80s. So there’s so much Abby (her character) would have forgotten.”

Not, however, how to deal with bullies. As her new friend Owen (Kodi Smit-McPhee) is chased, abused and assaulted by his peers, Abby is the one with the adult perspective.

“You’ve got to stand up to them,” Abby warns. “Stand up to bullies respectfully,” Moretz hastens to add. You never know when that kid you’re tormenting “has a vampire as a best friend,” she says, laughing.

Not that she didn’t scare herself.

“When I had all the prosthetics (fangs, contact lenses) on, all the gooey blood makeup and stuff, it’s crazy to look at yourself in the makeup mirror,” she says. “But having all that stuff on makes you feel that you’re not that person. I have to remember, underneath it all, I’m just Chloe.”

Moretz, a native of Atlanta, goes to some pains to reinforce that point, that she’s still a “little girl,” still “just Chloe.” So no matter how grown-up seeming the roles, the only parties she’s going to are “birthday parties, not crazy parties.” She keeps the Diana Vickers pop on her iPod and her crush on Justin Bieber, something she confessed to Ellen DeGeneres last spring.

Well, maybe the “Bieber Fever” has passed.

“Justin had his chance,” she says with a giggle.