You can try to explain Judy Blume in numbers: her books for children have sold 90 million copies worldwide, most famously Are You There God? It’s Me, Margaret. Over a 54-year career she has won more than 90 literary awards and been translated into 32 languages.

But this doesn’t explain her impact on generations of children, particularly girls. Blume, more than any other author before or since, taught kids about masturbation (in Deenie), menstruation ( … It’s Me, Margaret) and sex (Forever). She reassured them that hating your younger sibling sometimes is normal (Tales of a Fourth Grade Nothing) and that terrible things can happen to good kids and they’ll survive (Tiger Eyes). Most of all she taught them that it’s fine to be exactly what they are: ordinary kids.

Margaret even explicitly begs God to let her be “normal”, by which she means go through puberty. This moment is captured in the delightful upcoming film adaptation of Are You There God? It’s Me, Margaret, starring Rachel McAdams and Benny Safdie as Margaret’s parents, Kathy Bates as her grandma and Abby Ryder Fortson as Margaret. I tell Blume how strangely thrilling it is to see a movie about children where none of them are in possession of magical powers. “Yes, children are so used to superheroes now, aren’t they?” she says. Even in J. K. Rowling’s Harry Potter books the kids are magic, and I love those, I say.

“And I love her,” Blume immediately interjects. “I am behind her 100 percent as I watch from afar.” Blume is referring to the abuse Rowling has received for speaking up in defense of women’s sex-based rights, and given that Blume has faced repeated attacks since the 1980s, for her books’ descriptions of adolescent sexuality and puberty, she knows what it’s like to be pilloried as an author.

Has she reached out to Rowling? “No, no. I met her very early on in her Harry Potter career, and she said to me, ‘Oh, my sister and I used to read all your books,’ and she talked about Deenie. I think once or twice we sent each other little notes. But I haven’t been in touch with her during this tough time. Probably I should.”

Judy Blume, more than any other author before or since, taught kids about masturbation, menstruation, and sex.

Blume is talking to me from her home in Key West, Florida; her beloved husband, George, is on a sofa next to her “as my tech guru”, until he is shooed out of the room for playing a noisy game on his phone. She is — she says with some astonishment — 85, but sharp as ever, asking after my children, even though the last time we met was seven years ago, and she catches me out when my eyes start to wander around my computer screen. “What are you looking at?” she asks, half rebuking, half curious. (It was the countdown clock on my Zoom, boringly.)

She retired from writing in 2015, after the publication of her adult novel, In the Unlikely Event, but just as Blume stepped back from the limelight the limelight chased after her.

“My son Larry used to say to me, ‘When your fans grow up and get into power in Hollywood, you’ll see that they’ll make your movies,’” Blume says. As well as the forthcoming film, this month Amazon releases its rightly adoring documentary Judy Blume Forever, in which women such as Molly Ringwald and Lena Dunham describe the influence Blume’s books have had in their lives.

Kathy Bates and Abby Ryder Fortson in Are You There God? It’s Me, Margaret. Judy Blume insists the film is better than her book.

Superfudge is being turned into an animated series for Disney+ and Netflix is planning a series based on Forever, while Peacock — NBC’s streaming service — is producing a series based on Summer Sisters, Blume’s 1998 novel for adults about a female friendship. But perhaps the most surprising thing is that this adaptation of … It’s Me, Margaret is the first big-budget film version of a Blume book.

There had been a few television adaptations of Blume’s books before. “Spielberg had the rights to Superfudge, you know,” Blume says. “I greatly admire him and his work, but it did not work out. He was not there for Fudge and I was not happy.” This was the tepid 1990s TV series that Spielberg’s company, Amblin, produced. Blume didn’t like that it was live action (“I always thought it should be animated”) and didn’t like the pilot’s director, Bob Clark, and the show lasted for only two seasons. “Anyway, Fudge survived,” she says with a shrug.

By contrast the director-writer Kelly Fremon Craig understood … It’s Me, Margaret so well that Blume insists the film is better than the book. “The book is what it needs to be, in that it’s all from Margaret’s point of view, so you don’t know anything about the parents. But in the movie we get more of them,” she says.

“I am behind her 100 percent as I watch from afar,” says Blume of J. K. Rowling.

Small tweaks aside, the film sticks very closely to its source material, even keeping the early 1970s setting, because, Blume says, “you just can’t update this story to now, with cell phones and all the electronics. It just wouldn’t work.” She says it’s a movie for adults nostalgic for the time they read … It’s Me, Margaret as a child, but I see it as closer to something like Gilmore Girls, a nostalgia experience that mothers and daughters can enjoy together.

It also keeps in all the details — adolescent lust, the chat about menstruation, Margaret’s anxieties about religion — that have caused the book to be attacked multiple times by right-wing religious groups, alongside other Blume books for similar reasons. Blume has long been a courageously punchy critic of these groups, and just the day before she and I talk it was reported that Florida politicians are considering a ban on any discussion of menstruation in schools’ sex education before the 6th grade, when children are 12.

“It’s so bad. If it was bad in the 1980s, this is triple quadruple that, because this time it’s coming from the government, who are making laws. They say they want to protect kids, but it’s more like they want them to not think or ask questions,” she says.

It’s strange how the attacks on you have come from the right, whereas the ones on Rowling have come from the left, I say. “You would probably know better than me, and I’m not up on every word that’s been said. But it can also be said that [Rowling’s] a victim of Twitter, because people believe what they read on Twitter, whatever you actually said,” she says.

The important thing, she continues, is that people keep speaking up — and for that reason she recently said in an interview, for the first time, that she had two abortions during her brief second marriage (George is her third husband).

“I didn’t intentionally not speak about it before. But it’s really, really important to speak about it now.” Because of the overturning of Roe v Wade? “Yes, and I was there the first time around, and in the 1980s when the book banners really started. There aren’t a lot of us left who were there then, and if you weren’t on the front lines you don’t know what it was like.”

Blume does know. And in her ninth decade she’s still fighting.

Are You There God? It’s Me, Margaret hits theaters on May 19

Hadley Freeman is a writer for The Sunday Times