Male characters are twice as likely to take leading roles in children’s picture books and are given far more speaking parts than females, according to Observer research that shines a spotlight on the casual sexism apparently inherent in young children’s reading material.

In-depth analysis of the 100 most popular children’s picture books of 2017, carried out by this paper with market research company Nielsen, reveals the majority are dominated by male characters, often in stereotypically masculine roles, while female characters are missing from a fifth of the books ranked.

The 2017 bestseller list includes perennial favourites The Gruffalo, Guess How Much I Love You and Dear Zoo, in which all the animals are referred to by a male pronoun, as if by default. This approach to gender is equally present in more recently published bestsellers such as You Can’t Take An Elephant on the Bus, The Lion Inside, Supertato, The Day The Crayons Came Home, The Koala Who Could and There’s A Monster in Your Book – none of which contain any female characters.

The lead characters were 50% more likely to be male than female, and male villains were eight times more likely to appear compared to female villains. Only one book, Peppa and her Golden Boots, portrayed a sole female villain, acting alone: a duck who steals Peppa Pig’s boots and takes them to the moon. Over the course of each book, the characters who got an opportunity to speak were 50% more likely to be male than female, and male characters outnumbered female characters in almost half the stories that made it into the top 100.

Peppa and her Golden Boots is the only book in the top 100 to feature a lone female villian, a duck who steals Peppa’s boots. Photograph: PR Company Handout

Twice as many of the characters who were given a speaking part and a main role in the story were male – and, on average, there were three male characters present in each story for every two females featured. Sometimes this ratio can be far higher; Mr Men in London, for example, has 13 male characters and just two female. It was published in 2015.

“The research doesn’t surprise me,” said children’s laureate Lauren Child, author and illustrator of the Charlie and Lola picture books. “We see it in film and TV as well. But it gives out a message about how society sees you. If boys get the starring roles in books – both as the good and bad protagonists – and girls are the sidekicks, it confirms that’s how the world is and how it should be. It’s very hard to feel equal then.”

The research shows only 40% of characters given a gender were human – the rest were, for example, animals, birds, crayons, vegetables and skeletons. Among these creatures, the gender bias was even more marked. Whenever an author revealed a creature’s sex, it was 73% more likely to be male than female.

Furthermore, males were more typically embodied as powerful, wild and potentially dangerous beasts such as dragons, bears and tigers, while females tended to anthropomorphise smaller and more vulnerable creatures such as birds, cats and insects.

Deirdre McDermott, picture books publisher at Walker Books, said many of their new titles do feature strong female characters but unfortunately did not make the bestseller list. Out of the top 100, only half the titles were published in the past five years. “Parents go back to books they know and trust from their own childhood. They should seek out recommendations for new titles. If anybody wanted to put a weak girl in one of our books, I’d whack them over the head.”

New titles which break with tradition can certainly sell well: Julia Donaldson’s The Detective Dog, in which a brave female dog helps out a male sidekick and a male teacher, was the No 1 bestseller last year. Yet the Observer analysis shows that even modern bestsellers are not exempt from stereotyping. Authors and illustrators have continued to exclude all female characters from nearly 20% of the bestsellers published over the past five years.

Nick Sharratt, bestselling children’s author and illustrator of books such as Shark In The Park and Don’t Put Your Finger In the Jelly, Nelly said he thought that fact was “incredibly surprising to hear in this day and age”. “I do think about the ratio of male to female characters – I see it as part of the job. You never forget the picture books you enjoyed as a child. They stay with you for the rest of your life.

“Authors and illustrators have fantastic opportunities to break down stereotypes. We need to tackle these issues and at the moment it seems not enough is being done.”

The Observer research chimes with the results of a survey of 1,444 clothing items in 12 high street chains published by gender equality campaigners Hannah and Leo Garcia last week. It found that the animals on boys’ clothing are more likely to be fierce predators such as lions and sharks, while girls’ clothing usually features small, harmless, domesticated animals – effectively, their prey.

Jess Day, who campaigns to end gender stereotyping with the Let Toys Be Toys movement, found the research troubling. “If a wolf or a T. rex were a ‘she’ the story would be just as good. We hear from a lot of parents who change the pronouns in books as they read aloud.

“It is preparing children to see male dominance as normal, so that when women do less than half of the talking, that feels like too much to some people. And wWith so few female roles, there’s also not enough space for the female characters to be multi-dimensional. I think the lack of female villains reflects a wider cultural discomfort with women who are not well-behaved and good.”

Female adults undertaking caring roles were common in the stories, and there were twice as many female as male teachers. Mothers were also present almost twice as often as fathers. By contrast, fathers barely featured at all unless accompanied by a co-parent, appearing alone in just four books. “This reflects a skewed version of the world which is bad for boys as well as girls. The lack of fathers, for instance, steers them away from an interest in nurturing and caring behaviour,” said Day.