Atlantic for Kids’ new play explores sibling relationships, using the delicate weavings of a Hawaiian craft.Every good story requires a thread. Some writers have difficulty finding theirs, but not Lee Cataluna. The line that runs through her latest play, “Heart Strings,” comes from the real knots and tangles of a centuries-old Hawaiian craft.That technique, known as hei (pronounced HAY), consists of creating figures and patterns by manipulating a single loop of string. Although often compared to cat’s cradle, hei is more than a children’s game; it is a symbolic language. Each design has meaning: for instance, a star, the moon or the night becoming day.Seated at an outdoor cafe table on a recent afternoon in Manhattan, Cataluna, who is of Portuguese and Indigenous Hawaiian ancestry, placed a cord around her hands. Deftly moving her fingers, she transformed the string into a narrow rectangle with two triangles at its center.“So this is the house, right?” she said of the rectangle. “Then it breaks apart, and the two children run away.” She pulled her hands wide, and the triangles shot in opposite directions, then disappeared. “That’s the story I have to write,” she said she thought when, during research, she discovered this traditional hei. “I have to figure out what that means.”Different characters create that hei and others in “Heart Strings,” which runs through Oct. 23 at the Linda Gross Theater in Chelsea. Presented by Atlantic Theater Company as the first Atlantic for Kids production since the pandemic lockdown, it welcomes young audiences — the public on weekends and school groups on weekdays — with a drama that is both culturally specific in its details and universal in its themes.“I thought about what kind of issues would resonate with kids and their parents,” Cataluna said. Sibling rivalry immediately sprang to mind.But in “Heart Strings,” the meaning of “sibling” is complicated by another cultural tradition. The play’s central characters — Hoku, 10, and Mahina, 6 — are sisters according to hanai (huh-NYE), a Hawaiian custom in which couples take in children who are not their own. Hoku’s grandparents are raising both girls, and the reserved, studious Hoku, who once welcomed the infant Mahina into the family, now resents the high-spirited, questioning kindergartner she has become.“You’re not my real sister,” Hoku says, shutting out the younger girl with a force that threatens to shatter their household as utterly as that hei collapsed in Cataluna’s hands.Born on Maui, Cataluna remembered hei, but she did not choose it as a recurring motif to dazzle New Yorkers. She originally wrote “Heart Strings” for her teenage son’s theater group in Honolulu. His school had requested a play incorporating something tangibly Hawaiian, much as Kathryn Schultz Miller’s “A Thousand Cranes,” which the students had previously performed, celebrates Japanese culture through origami.When the coronavirus pandemic ended the school’s plans to present “Heart Strings” at the Edinburgh Festival Fringe, Cataluna successfully submitted her work to ReImagine: New Plays in TYA. (TYA stands for Theater for Young Audiences.) Established by a consortium of theatrical organizations, ReImagine awarded grants in 2021 to playwrights who were Black, Indigenous or people of color. As a grant winner, Cataluna could also select a participating theater company to workshop her play.She felt immediately drawn to Atlantic, which was also eager to acquire “Heart Strings” and is now giving it its world premiere: Here was a play that highlighted a culture that was part of America but that was almost never explored onstage.“It’s so three-dimensional, the storytelling that happens in the hei,” Alison Beatty, the artistic director of Atlantic for Kids, said in a post-rehearsal interview. After the pandemic’s isolation, she added, “having something that was tactile — that you could feel with your hands, and that was such an integral part of how the story is told — really appealed to me. And then, I think, just the questions that are asked by the play: what it means to be family, what it means to be at home.”Aczon, far left, in a scene from the Atlantic for Kids production, with, clockwise from top left, Jeremy Rafal, Kristi Donna Ng and Un Joo Christopher.Julieta Cervantes“Heart Strings,” which is directed toward children over 6 — an older audience than most Atlantic for Kids offerings — also gave the company a rare opportunity to help shape a playwright’s vision instead of importing a finished production. Beatty, for instance, suggested adding hula gestures, another form of choreographed storytelling, to the production. John-Mario Sevilla, a hula scholar, then taught some movement to the cast.The script also evolved. Cataluna had set her earliest drafts in the present, but after her son’s classmates asked why the characters were playing with string when they had cellphones, she switched the action to the 1930s. She also wanted to highlight the pressure on Indigenous peoples to assimilate. Hoku, played by Sienna Aczon, doesn’t mind using an English name and words at school; Mahina, portrayed by Un Joo Christopher, rebels against those rules. (Almost all the actors in the Atlantic production have lived in Hawaii.)“In my father’s era, and before his, Hawaiian was not allowed to be spoken in the public schools,” Cataluna said. She drew on her family’s past again in a scene in which Hoku’s friend Josiah (Aaron Banes) reflects on his love for his Hanai sister, as Cataluna’s father once did.But she has resisted acknowledging another autobiographical detail as more than mere coincidence: She has a younger biological sister from whom she is estranged.“One of my best friends keeps calling me on it,” Cataluna said, noting that he pointed out parallels to her play. She and her sister haven’t reconciled, but, Cataluna added, “if she ever needed a kidney, I would give her my kidney.”Audiences, however, don’t need to have siblings to recognize how vulnerable — or how steadfast — the bonds of love are, Kat Yen, the production’s director, said in the same conversation.In families or friendships, “we delve into struggle, we delve into confrontations, but you never lose the love,” Yen said. “Somewhere in there is a message that I’m interested in for the audience.”But that isn’t all that children take home: The company provides instructions on how to make a hei. More