Billy’s family was not what you’d call ordinary,” is the start of Jodie Lancet-Grant’s debut picture book published this month, an opening guaranteed to engage any kid who has ever felt the slightest bit different — whether that’s because they are Jewish, speak a non-English language at home, or, like Lancet-Grant’s six-year-old twin daughters, they have two mums.

And you might think that’s what marks Billy’s family out as different, as he too has two mums. Except it isn’t. His mums are different because they love to dance jigs and sing sea shanties, they have a parrot called Birdbrain, they use smelly old maps to find their way and their house sports nets and an anchor. In short, they are pirates, and although they hide their idiosyncrasies on a school sailing trip — to spare Billy embarrassment — when Captain Fishface gets stuck in the toilet, the pirate mums come to the rescue.

It’s a rollicking good read, and it fills a gap in the market that Lancet-Grant spotted when she first started to look for books for the twins with families like their own. “I don’t want to denigrate some of the books that were out there,” she says, “but some just weren’t the kind of books I was expecting.” Some had old fashioned illustrations, and others framed LGBT families as different from the norm. “I didn’t even want to introduce the fact that we were ‘different’ and ‘other’ to the girls.” So her wife, Sam suggested she wrote her own. And Lancet-Grant took the challenge.

It helped that she’d done some writing and journalism, and worked in publicity for a children’s book publisher. She found an agent, and wrote her first book, which brought her to the attention of some editors. One editor suggested that to make the idea “less frightening” for the industry she should take something known and trusted in children’s books and put a LGBT spin on it. “That’s when I came up with the idea of using pirates. The idea did come quite fully formed … I wanted to play a little joke on the readers that they would think that a family is different because they have two mums. And actually it’s because they’re pirates.”

She’s well aware that 30 years ago Section 28 was introduced by Margaret Thatcher, banning the promotion of homosexuality in schools. It meant that books like hers would have been banned from schools — and it was only overturned 20 years ago. She also knows that in some Orthodox Jewish schools children are still not taught about families with two mums or dads. She says it is “jaw-dropping” that it would have been illegal to talk in schools about “the family that I have, this wonderful loving family, that my girls are so happy in.” She’s happy that Oxford University Press chose to publish the book, as it has excellent links with schools, and she reports “great feedback” because “most parents do want to show their children all these kinds of families, and do want to show them an inclusive world.”

Lancet-Grant and Sam, a civil servant, met at university in Leeds and live in Walthamstow, north London. They are both Jewish, and wanted a Jewish wedding. “Neither of us are very religious at all. But the culture is very important to us, and we wanted a Jewish element to the wedding. But because ten years ago civil partnerships were legal and [same sex] weddings were not, our rabbi didn’t have the power to actually marry us.” So the registrar performed the legal ceremony and the rabbi had to wait until they left before she could arrive and the chupah was put up and the Jewish wedding took place.

Their daughters, Alexa and Delilah, are “very proud” of the book. There are only a handful of Jewish children at their primary school, so their mums are also thinking about how to introduce their classmates to Judaism, and buy them children’s books with Jewish themes and characters. “One of the reasons it’s so bad not to have diverse characters and people from all sorts of backgrounds in books is because people learn subconsciously if they don’t see themselves in a book that they’re not worth telling a story about. Their life isn’t worth depicting. And so I think it’s so important to change that, and to do whatever is possible to change that, especially when you see the effect it has on children as well.”

And do her twins have pirate mums? Lancet Grant laughs: “You know, I wasn’t really very into pirates before this book, but then I started doing research and I found out about all these famous women pirates, and I remembered that when I was a kid I used to love female pirates.” She points out that in most children’s books pirates are all male, with maybe one female — “Smurfette syndrome” — and that’s a shame. But it’s all secondary to the story. “I don’t want people to think of the book as being an issues-heavy book with a lesson. I want them to think it’s a fun adventure story full of quick thinking and funny characters and drama, and a heart-warming ending that just happens to have two mums and represents a different kind of family.”

The Pirate Mums is published by Oxford University Press