As a little girl in the 1970s, there were two people I wanted to be. One was Agnetha Faltskog from Abba and the other was Roberta from The Railway Children.

Miming to my mum’s Abba records, using the living-room rug as a makeshift Top Of The Pops stage, I became Agnetha.

Watching Lionel Jeffries’ definitive version of The Railway Children countless times, I imagined myself as Roberta; sitting on walls waving at trains, averting disaster by tearing up red petticoats, and running along the steam-filled platform of Oakworth station.

Edith Nesbit’s story of a suburban family moving to rural Yorkshire, captured in that lovely 1970 film, is close to many hearts, mine included. I know every scene off by heart and I never tire of it.

In the case of The Railway Children, the over-used terms ‘iconic’ and ‘timeless classic’ are justified.

It’s unashamedly sentimental, but it’s more than just a tale of three children, a railway and that tear-jerking Daddy scene at the end.

It’s about lost innocence and the simple pleasures and confusions of childhood, caught up in the hazy days of an Edwardian summer. It’s a snapshot of an era soon to be shattered by the First World War. I’ve made a point of showing the film, on DVD, to my niece and nephews from an early age and they’ve each been engrossed in the story.

Jack, seven, is a particular fan, and not just because he loves trains. Like me, he knows it practically scene-by-scene and I’m often required to rewind his favourite bits – Peter’s model steam train blowing up, Ruth the housemaid turning nasty after getting a soaking, the tunnel paper-chase, the sliding trees, and the hapless brass band playing on the station platform – for repeated viewings.

Jack and I watched it together one recent rainy afternoon and, while I was in the kitchen getting him some juice, I heard him muttering “I dare-say”, imitating the gruff old horse-and-cart man who takes the family to the Three Chimneys.

That’s the kind of moment I’ll cherish when Jack is too cool to spend rainy afternoons watching The Railway Children with his auntie.

For now, I’m looking forward to him seeing it on the big screen. It speaks volumes for the film’s enduring appeal that, to celebrate its 40th anniversary, it has been remastered for future generations to enjoy.

On Sunday its stars, Jenny Agutter, Sally Thomsett and Bernard Cribbins, gathered in Bradford for the premiere of the digitally-enhanced version. “It means the film has an ongoing life,” said Jenny Agutter. I dare-say Jack would agree.