When Sarah Yarnold posted a photo on Facebook of her seven-year-old daughter Darcy grinning and holding up a pair of muddy football boots, she didn’t expect thousands of people across the world to see it. But the accompanying caption, telling how Darcy’s passion for playing mixed football outshone the unkind comments of a handful of boys and their parents, pulled on the heartstrings of many ordinary people who were moved to share their own stories.

Yarnold’s message, originally shared by Ulster rugby player and family friend Sorcha Mac Laimhin, highlighted the behaviour of some opposition parents watching from the sidelines and their sons, who refused to shake Darcy’s hand after the match. Yarnold wrote: “She has to deal with cruel comments from other teams and their parents about our lovely lot having a girl playing on their team.”

Some of the biggest names in sport posted messages to Darcy in response – from England’s greatest ever female player, Kelly Smith, to sports minister Tracey Crouch, England gold medal hockey winner Sam Quek and TV presenters Jacqui Oatley and Michelle Owen, many of whom had experienced sexism while playing or commenting on the beautiful game.

When the England women’s team official account, the Lionesses, tweeted Yarnold to ask if Darcy would like to be a mascot at their match against Sweden next month, the story took off. Suddenly there were TV requests, radio requests, newspaper requests – everyone wanted to speak to Darcy and her mother. It was overwhelming.

“I wrote a little thing about one little girl,” says Yarnold. “The story has travelled because lots of other little girls have had their experiences. It’s gone big because Darcy is not the only one – that’s what’s carried the story, because it’s resonated so much.”

Back home in Bispham, Blackpool, over spaghetti hoops on toast, Yarnold explained to Darcy that she would be leading out the Lionesses at their next home game. “I just said, ‘Woah,’” remembers Darcy, “I felt excited and happy, but a bit nervous – because people will watch me. I’ve only seen mascots on the TV before and I thought they were kind of brave.”

Darcy in action on the pitch.

Women’s football has gone mainstream in Darcy’s lifetime – the newly structured Women’s Super League is now professional with all players training full-time, and the dream of a professional football career for women finally a reality, albeit with a seemingly insurmountable gender pay gap. A record crowd of 45,423 was at Wembley this year to watch Chelsea beat Arsenal in the FA Cup final, and millions are tuning in to watch the Lionesses play on TV.

Darcy – nicknamed “Edgar Darcy” by one of the team’s parents after the Dutch midfielder Edgar Davids who, like Darcy, wore glasses when he played – is part of a generation of girls growing up with football as a genuine option. She plays five days a week, a passion ignited by chance when a coach visited her reception class at school and gave a taster session. She joined Bispham Junior Football Federation and football soon became the focus of family life.

Her father David – a joiner by trade – took his coaching badge and began working with Darcy’s team, the Spartans, as well as coaching the club’s girls’ team, the Phantoms, for whom Darcy also plays. “People always ask, ‘Is that why Darcy plays, because Dave coaches?’” says Yarnold, “and we say, ‘No, Dave coaches because Darcy plays!’” She laughs. The family’s back garden has been transformed into a football pitch with mini goals and fake turf. Meanwhile Sarah, a beautician, ferries Darcy to training and matches, as well as swimming and taekwondo. Older siblings Cleo and Eailligh never caught the football bug, but are immensely proud of their little sister.

It was Yarnold’s pride at how her daughter brushed off the upsetting incidents that prompted her to share their experiences. “One of Darcy’s favourite parts of the game is shaking all the hands, she thinks it’s brilliant. She’ll shake their hand and say something like ‘Good job!’ or ‘Hey, you were great today!’ She just buzzes off it. So when I see her put her tiny little hand out, and someone looks at it and turns away, I see her face go, ‘What did I do?’ I just have to reassure her that this isn’t about her. There is a minority of people who still believe that the football pitch is only for boys.”

Certainly there is still some way to go before women involved in the beautiful game are fully accepted. Quek’s views on a football line-up this month earned her vitriolic abuse, and despite widely praised performances as a Sky and BBC pundit, Alex Scott was recently trolled by former Chelsea and Brighton striker Leon Knight for being a “woman pundit”. Equality campaign group Women in Football recorded a 400% increase in the reporting of sexist abuse faced by women in the industry last season.

“I don’t want her to linger on it,” says Yarnold. “It’s such a small part of her playing football. The important thing is she’s loving it – and she’s now got a wonderful opportunity to go and meet some really inspiring women.” The family are moved by how supportive Darcy’s teammates have been. “Blackpool FC have invited her whole team for a visit, which is amazing, because this is what it is about. We want to show how grateful we are for how amazing the boys on her team are.”

On Friday, the family joined former Manchester United captain Michael Carrick on BBC 5 Live, with Darcy invited to be a mascot for the newly-formed Manchester United women’s team on Sunday .

Yarnold says the interest has been great but she’s looking forward to returning to normality. “If this has taught me anything it’s that I love my quiet, normal, happy, chasing-around-after-the-kids life. It’s the best.”