Think of “Topside” as a subterranean “Beasts of the Southern Wild.” A child, growing up isolated, knowing only her immediate surroundings and her sometimes-absent parent, lets us see this “mole people” existence through her wide, unblinking eyes.

Co-writers/directors Celine Held and Logan George take us into the bowels of New York city for a tale of clinging, paranoid motherly love and a five year old child’s first experience of the world above. It’s a moving, harrowing film that hangs on a beatifically transparent performance by screen newcomer Zhaila Farmer.

As “Little,” she’s a child who has only the vaguest notion of what “stars” are.

“Stars don’t come down this far, baby,” her mother (co-writer/director Held) has to tell her. It may be dark where they are. But that’s far below ground in an abandoned subway tunnel, so deep you have to climb up to get to the tunnels where trains still run.

We see Little wander amongst the homeless squatters who have set up housekeeping, cadged electricity for phone chargers and the portable video player Little stares at when she isn’t petting the caged dogs or acclimated cats that others keep as pets, when she isn’t looking for something to eat/

Mom dotes on her and enfolds her in affection when she’s there. But she’s not around much. She’s “Topside,” looking for a fix or begging, bargaining for sex work to earn the cash for a fix.

Nikki tells Little that she’s “trying to find a place for you and me up top,” but she’s waiting until Little’s wings have sprouted. What she means is she’s trying to get around them being discovered by the system.

Neighbor John (Fatlip), who takes enough interest in the kid to make us wonder if he’s her father, feeds Little and berates Nikki at every turn — her begging for drugs, her neglect of the child, who “needs to be in school.” As we’re seeing most of this from Little’s point-of-view, we mostly hear these arguments, at least at first. Little’s is a world of sound and darkness.

But “the system” is closing in around them. Authorities are about to re-open this tunnel, and she sees their flashlights and hears their walkie talkies. Eventually, they’re going to find and evict them.

George and Held give us a child’s sense of wonder, and terror at the unknown, when Little comes to the surface. And they stare, unblinking, at the “homeless by choice” subculture — disturbed, addicted, paranoid people who might duck into a soup kitchen but duck back out if anybody asks them anything about themselves.

Held’s performance as an addled addict helpless to focus on anyone other than herself is gripping. Nikki’s struggle tells us that she’s aware of how she’s failing, but clumsily hellbent on improving their situation unless that means she has to deal with authorities who will take her kid.

Farmer is a radiant presence, our eyes and ears experiencing this alien world and a sheltered child’s way of looking at what to us might be familiar but to a kid could be potentially terrifying — trains, crowded subway cars, a cacophony of chatter, PA announcements and thundering machinery. The chaotic streets above are even noisier, with the added shock of bright light.

“Topside” ably covers the basics of homelessness — public restroom clean-ups, hand sanitizer “baths,” hunting for a phone charger (Even the homeless have iPhones in the movies, a tone-deaf blunder I see again and again.), the nameless sense of “community.

And by putting us in the child and mother’s shoes, the film becomes a thriller, full of fear, anxiety and desperation. We fret over what might happen to Little, what fresh horror awaits Nikki and what dangers a careless but adoring mother will next expose her five year-old to.

Rating: unrated, drug abuse setting, implied sex work, profanity

Cast: Zhaila Farmer, Celine Held, Fatlip, Jared Abrahamson

Credits: Scripted and directed by Celine Held and Logan George. A Vertical release.

Running time: 1:30