“They’re literally my brother and sister,” Greenblatt says of Heaven, 19, and Hendrix, 16

Ariana Greenblatt was only 13 years old when she set off to Budapest, Hungary, during the COVID-19 pandemic to film for the sci-fi action-comedy Borderlands.

At the time, Greenblatt, who’s starring in the movie alongside Cate Blanchett, Kevin Hart, Jamie Lee Curtis and Jack Black, was the only kid on set for several months at a time — that is until Hart’s kids, Heaven, 19, and Hendrix, 16, came to visit.

“I met them on set because I hadn’t seen kids in four months. It was just straight adults. Then Kevin was like, ‘Hey, I’m bringing my daughter. She’s on FaceTime.’ She’s going to hate me for telling this story. So he’s on FaceTime with her. And I was like, ‘Oh my God, hey.’ And she starts freaking out. I’m like, ‘Oh my God, you’re making me feel famous,’” Greenblatt, 16, says in PEOPLE’s August digital cover story.

Once they met in person, their connection was instant.

“We bonded and we’d paint rocks together and they’d eat lunch in my trailer every day,” she recalls. “It was this crazy bond and connection instantly… they’re literally my brother and sister. I love them so much.”

It was unexpected for Hart too. “[My kids] were lucky enough to bond with the only other kid there,” he says, noting that the trio “ended up spending an astronomical amount of time together, stayed true to their friendship and built off of it. Good people attract good people. I think that’s how they found each other.”

Four years later, Greenblatt remains an honorary member of the Hart family — and she calls the Jumanji: The Next Level star “Uncle Kev.”

“She’s around my house all the time. This whole ‘Uncle Kev’ thing pisses me off but she won’t stop doing it,” Hart, 45, quips.

All jokes aside, Greenblatt knows that he has her back.

“He believes in me so much. Anytime I’m at his house and his friend is there, he’s like, ‘This is Ariana. She’s the next big thing.’ He just makes me feel really good,” she says.

And he really means it: “What I really admire most about her is that there’s no fear,” says Hart. “I’m glad we were able to bond and get close but I’m excited to see what she’s gonna bring to the business. More importantly, do for the business.”

In Borderlands, Greenblatt plays Tiny Tina, a wild tween on the run across the universe with a penchant for swearing and blowing things up. At the time, she leaned in to the role.

“If that movie was rated R, which I pushed for it to be, you’d hear more of my personality,” she says of the PG-13 film. “I swear a lot. And I do the middle finger too much. I have to stop because I’ve been told to.”

She adds, “While I was filming, I just felt so free — like I could say and do whatever and it would work because Tina is that unpredictable feral girl.”

Borderlands is now in theaters.