Pippi Longstocking turns 70 this May (though she doesn’t look a day over 10!) but fans of her creator will be getting the gift: reissues of two out-of-print classics by Astrid Lindgren. The New York Review Children's Collection will publish Mio, My Son (1954) and Seacrow Island (1964), stand-alone novels that were among Lindgren’s most popular works.

At the time of its initial release, Mio was critically acclaimed, winning the German Youth Literature Prize in 1956, and becoming the basis for the 1987 film, Mio in the Land of Faraway, which featured 12-year-old Christian Bale as Mio’s best friend and Timothy Bottoms as Mio’s father.

“It was really the first children’s book written in Sweden that was taken seriously by the prominent people who reviewed literature for adults,” said Olle Nyman, Lindgren’s grandson and CEO of Saltkråkan AB (Saltkråkan is Swedish for seacrow), the company that manages her literary estate. “Before Mio, children’s books had been sort of looked down on as not quite worthy so this was a big step in Sweden for children’s literature.”

Seacrow Island had a very different genesis. It began as a popular television show, Vi på Saltkråkan, written by Lindgren, who set the series in a place she had grown to love: the Stockholm archipelago, 40,000 small islands in the Baltic Sea where thousands of Swedes vacation each summer. The main character is a widowed author, Melker Melkersson, who takes his four children to Saltkråkan Island, where they make friends and have many adventures with the year-round islanders.

“It’s a lovely story and I grew up watching the TV series being aired on Swedish national television, so it is very special to me,” Nyman said. “But it was a big challenge for Astrid because she had to first write the TV series, which she had never done before, and then she had to write the book, too. Luckily, it was a huge success.”

The TV series was remade into a feature-length film in 1968 but the original 13 episodes are re-run almost yearly on Swedish and German television. The popularity of the first film generated three additional full-length movies.

“It’s fitting because the island was the place she loved most on earth,” Nyman said. “She wrote a lot of her books there, writing by hand while still in bed. She loved to be there.”

The NYRB reissues are part of a big year for Lindgren, who died at age 94 in 2002 but left a catalog of nearly 100 novels, stories, plays, television and film scripts. Worldwide sales are approaching 150 million books, and in 2013, it was estimated that Lindgren was the third most translated children’s author, behind only Hans Christian Andersen and the Brothers Grimm.

Nyman said he did brisk business at the recent Bologna Book Fair, with many of Lindgren’s foreign publishers planning special events for Pippi’s 70th birthday, on May 21. “Many of our publishers are doing anniversary editions,” he said, “and Swedish embassies all over the world will be celebrating.” Next month, Saltkråken will also mark the publication of a “new” work by Lindgren, The War Diaries, 1939-1945, an account of life in Sweden during World War II that was found in Lindgren’s apartment after her death.

“This is something she wrote before she was famous, keeping this diary from the start of the war until the end,” Nyman said. “The style is the same as in the rest of her books but her point of view is so interesting. It is a masterpiece.”