Interest trickled in slowly after the script’s publication was announced in February, Ms. Gannett said, but in the past week, requests for reserved copies nearly doubled.  In New York and across the country, so-called Potterheads swarmed bookstores Saturday night and into Sunday morning to celebrate the release, as if they had found the secret winged key that not only let them back into their childhoods but also opened the door to another generation.  Judy Stelter, the manager of Book World in Sturgeon Bay, Wis., was expecting a smaller, older audience for the store’s midnight party. Instead, she was greeted by teenagers and young children with their parents, who filled the small store to enjoy cake and chocolate frogs (a treat among wizards).  “Look at all the young kids in here,” Ms. Stelter said, standing beside boxes of “Cursed Child.” “They’re in here for a book that’s in print and on paper, not on an electric device. Once they read like that, they’ll read for life.”  Many fans happily brought family members who were not old enough — or even born yet — for the celebrations of the original series.  In Atlanta, Erin Whitlock, 24, brought her 12-year-old brother Liam to a Barnes & Noble in the Edgewood neighborhood.  “He’s as big a fan as I am, and it’s just really cool to be here tonight because he gets to experience what I grew up with,” Ms. Whitlock said, noting that her brother visits Ms. Rowling’s website Pottermore, where she regularly publishes new stories. “The wizarding world doesn’t stop with the books. It goes with your imagination.”  JillEllyn Riley, 48, a writer and editor who lives in Cobble Hill, perused the novels at BookCourt with her sons, ages 13 and 19, who did not seem to mind the spectacle of their mother dressed as Sybil Trelawney, a professor at Hogwarts. Ms. Riley said she hosted monthly Harry Potter club meetings in the neighborhood with her younger son.  “We came here to BookCourt for Book 7, all of us,” she said. “My 13-year-old was 3, and I knew that later he would read the books and wouldn’t be able to go to the midnight releases, but I knew he’d know he had been there once.”  Aubrey Nolan, 25, who planned the evening at BookCourt, said she wanted to keep the activities family friendly. All around her, children sipped cream soda floats they passed off as butterbeer and decorated wands with paint, sequins and string. Others had mug shots taken that resembled the wizards imprisoned at Azkaban.  Bookstores around the country embraced the theme, too, with Books of Wonder in Manhattan offering photos with owls (like Harry’s Hedwig) and the Charles Deering Library at Northwestern University outside Chicago refereeing a Quidditch match, a sport played in the series.  At the Elliott Bay Book Company in Seattle, nearly 250 people showed up for what was billed as a Hogwarts reunion. And members of the Seattle Shakesbeerience performed the first few scenes from the play with Patrick Lennon — who said the group’s motto is “script in one hand, drink in the other” — as Harry.  “I’m in the group that aged along with Harry,” Mr. Lennon, 30, said. “One of the actresses says she’ll probably be crying through it. I might too.”  For some, nothing was more important than getting their hands on the newest edition, even if it meant waiting alone or interrupting a vacation.  Annie Grandidge and Travis Dicks, tourists from New Castle, Australia, spent two and a half hours in line at the Barnes & Noble on Fifth Avenue in Manhattan. And Ashley Johnson, 32, the actress who played Chrissy Seaver in the sitcom “Growing Pains,” recently moved to Brooklyn to work on NBC’s “Blindspot." She showed up at BookCourt by herself, knowing she would easily make friends with other Potter fans.  “I was a little angry that I didn’t read these as I was growing up,” Ms. Johnson said. “I found them in my mid-20s and I never got to go wait in line for the original books, so to be a part of that I felt like I needed to go do it. We don’t get to do this with a lot of things with how fast the world moves, and to wait in line for a book at midnight feels really special.”  Margaret Piraino, 24, dressed as Nymphadora Tonks, a half-blood witch, complete with rainbow hair and Potter-themed jewelry, attended the BookCourt party with her girlfriend, Laurel Detkin, a fellow Potter enthusiast. But this time was different.  “I grew up with Harry Potter and it’s been my entire life, and my dad would go to Barnes & Noble with me every time there was a new release,” Ms. Piraino, who lives in Brooklyn Heights, said. “And this year, my dad died in January and it’s the first time I had to go on my own.”  In Seattle, Dylan Blanford, 13, donned a long black robe and a yellow tie as a member of Hufflepuff, one of the four houses at Hogwarts, and said he was jealous that he was not at parties for the previous Harry Potter books. He started reading the books at age 5.  “I’m excited because there’s still this little 6-year-old jumping around inside of me going, ‘Harry! Harry! Harry!’ And there’s also this 13-year-old jumping around inside of me going, ‘Harry! Harry! Harry!’” he said. “I’m so excited because it’s not the end, forever, you know?”  Correction: July 31, 2016 An earlier version of a photo caption in the accompanying slide show reversed the positions of Katelynn Kenney and Liane Pippin. Ms. Kenney was on the right, not the left.  Reporting was contributed by Clay Bolton, Posey Gruener, Emily Palmer, Natalie Pita, Rita Pyrillis and Ryan Schuessler.  A version of this article appears in print on August 1, 2016, on page A18 of the New York edition with the headline: Long Lines, Costumes and an Owl Welcome a New ‘Harry Potter’. Order Reprints| Today's Paper|Subscribe
From Brooklyn to Seattle, fans of the book and film series turned out at midnight on Saturday for the release of “Harry Potter and the Cursed Child.”