From a transgender teddy bear to a fearless girl pirate, children's authors are tackling gender norms like never before, as debate rages about what it means to be a boy or girl.
Visitors at this week's Frankfurt book fair, the world's largest publishing event, will be faced with a string of books for young readers that defy stereotypes and navigate today's hot-button issues of transsexuality and gender fluidity.
Stories with transgender lead characters, in particular, have broken one of the last "taboos" left in children's writing, said literary expert Nicola Bardola.
"Some are watching this trend nervously, these kinds of books still make critics uncomfortable," Swiss-born Bardola said, an author himself.
One of the most headline-grabbing recent titles has been Introducing Tilly, a tender story about Thomas the teddy bear who tells a friend: "I've always known that I'm a girl teddy, not a boy teddy."
The picture book, aimed at children aged four and older, was written by Australian Jessica Walton who was inspired by her own father's transition to a woman.
Translated into German last year as Teddy Tilly, Bardola called the book "a phenomenon".
For a slightly older audience, there is US author Alex Gino's award-winning George, which is about a transgender 10-year-old determined to play a female part in the school play.
The book has won widespread praise for its warm portrayal of a feisty heroine, but it has also stirred controversy.
A Kansas district last month decided not to purchase George for the area's schools, deeming it inappropriate for young readers.
Gino, a self-described "genderqueer" - someone who refuses to be defined by a gender - promptly started a Twitter fundraising campaign to deliver copies to every school library in the district.
In just half an hour the money poured in.
"Books [based on transgender themes] should be judged by their literary quality and children should be given a chance to decide whether or not they want to read these stories." — literary expert Nicola Bardola
"Sharing stories of trans people with children is key to trans acceptance. There is no age before which it is appropriate to be compassionate," Gino told AFP.
In the young adult section, readers can find Meredith Russo's If I Was Your Girl, which chronicles an American teen's fresh start at a new school, burdened by the secret that she used to be a boy.
Children's book expert Bardola said the trailblazing tales had triggered much earnest hand-wringing from critics wondering whether it was "appropriate" or "dangerous" to introduce young readers to such complex themes.
He said it reminded him of the stir caused in the 1980s when gay characters started appearing in young adult books.
"The debate is nearly identical. You can tell literary critics are unsure about these (transgender) themes," he said.
"I think we can be a little more relaxed about it," he added.
"These books should be judged by their literary quality and children should be given a chance to decide whether or not they want to read these stories."
German literature critic Ralf Schweikert was more sceptical.
"If you want to talk about what it feels like to live in the wrong body, you are asking for a lot of self-reflection from young readers," Schweikert told AFP.
For bookworms scouting for a more general take on the gender debate, there's no shortage of new titles out to smash the patriarchy, reflecting a wider cultural discussion about the traditional roles pushed upon boys and girls.
"There are increasingly books for very young readers out there that deliberately challenge these gender stereotypes," Schweikert told AFP.
He listed the German early-reading book series Wild Wilma as a standout example, about the buccaneering adventures of a girl sailing the high seas as captain of a pirate ship.
'Ponies and princesses'
Bardola said stories that turned gender roles on their head had always been around but that such titles tended to peak every few years depending on the zeitgeist.
"Of course you can still find books for girls about ponies and princesses," Schweikert said.
"But if you want to get away from those cliches, there's a lot of good material out there right now."
And more titles grappling with gender issues are on their way.
Scholastic, which published George, will next year be releasing the young adult novel And She Was by Jess Verdi, about a teen coming to terms with a parent's transgender identity.
"And we've seen a number of trans or gender non-binary characters in other books we are publishing," said Scholastic's editorial director David Levithan.
Books, he added, that "show how gender diverse our real world can be