He says it's a special quality and when you see it, you know it. "You feel that ... when you go to these festivals and you meet like these massive actors [and] that same thing you feel with her."
Finding Hushpuppy was crucial because Beasts of the Southern Wild unfolds entirely from her perspective. Motherless, she lives with her wild, but beloved father Wink (Dwight Henry) in a bayou community.
When Wink becomes sick, an enormous storm floods her town and fierce ancient creatures are freed from the melting ice to find her. Hushpuppy becomes determined to save everything she holds dear.
Zeitlin says when they realised the weight of the film needed to be carried by a child, "we definitely were upset".
"It was just a new challenge to throw into the pot of a million impossible things," he says, so "finding her was this miraculous moment".
And finding her father, Wink, was just as lucky.
Zeitlin thought they would have to hire an actor, because it was such a difficult role. But the man to play Wink, Dwight Henry, ended up being right under their noses.
"He was the baker across the street from our casting office," Zeitlin says. "Every morning before we'd start casting for Hushpuppy and we'd eat donuts over there and get coffee."
He says Henry has a magnetic, charismatic presence and when they tested him with Wallis, they were blown away.
The reason Zeitlin says he and independent film-making company Court 13 were able to take a chance and cast unknown actors was because Beasts of the Southern Wild was financed by not-for-profit film production company Cinereach.
He says to be able to finance a film in the US, you usually need to be making a movie that fits into a genre like horror, or bring a huge star on board. Otherwise it's unlikely you'll find support.
"We had this very unusual type of funding where all these risky choices we wanted to take were encouraged," he says.
The film was shot in Louisiana, which has become like a second home for Zeitlin.
Although originally a New Yorker, he says he first found himself there to film the short Glory at Sea in 2006 and fell in love with the place and the people. He says it's since become something of a muse.
"I'm sure I'll make films in other places at some point but I have a whole laundry list of Louisiana films to make and I think we're [Court 13] going to be based there, have our company there, and just kind of make that headquarters, and that's going to be home."
What: Beasts of the Southern Wild
When: Opens today
- TimeOut / AAP