The young mum pushed her trolley through the fruit and veg section of Sainsbury’s.

Her small child sat in the front, arms wide, belting out Let It Go from the Disney film Frozen. As the little girl’s voice trailed off, her mum took up the chorus just as loudly to hit the high notes.

I don’t know about anybody else but it made me smile and start singing under my breath.

The film has been a massive success, aided and abetted by a stand-out song that defies logic. It has complex lyrics, it’s a song of rebellion, liberation, almost coming of age. It’s My Way for the under nines even if the under nines don’t know it.

The film version was sung by Broadway star Idina Menzel and won an Academy Award, the sound track album went triple platinum in America alone and it’s had 380 million hits on YouTube where it has achieved the accolade of being copied and parodied countless times and performed by other artists.

A spine-tingling version is that created by British-born Alex Boye with the One Voice Children’s Choir. He gives it an African tribal feel while filming in real snow and ice in Utah with 11-year-old Lexi Walker doing the lead vocals. It’s had 44 million YouTube hits.

It’s such a special song that when the film’s writers first heard it they re-wrote the ending of the movie. Until then, Elsa was going to be a pure villain. The song changed their minds and became a power anthem in a story where the message is true – love conquers all.

All children wanted to see the film and have the DVD, all little girls wanted the Anna and Elsa dresses and, most of all, everyone wanted to sing the song.

Even I, who could easily claim the title Old Grumpy Boots of 2015, have not been immune. My grand-daughter Jeannie is a massive fan and I have watched the film at least three times with her. She wears the dress and sings the song with all the actions, so it must be good. Experts agree.

Dr Vasco Hexel at the Royal College of Music says it has the kind of chorus that makes hit records.

“Even if I had only heard the song once, I’d remember that phrase,” he said.

A great song from a very good animated film with a positive message that had a young mum and her daughter singing out loud in a supermarket.

Mind you, I draw the line at the indulgence of a Middlesbrough mother who claims her three young children have watched the film on DVD 600 times in five months. Really?

That means the kids have been sitting in front of the TV for 7.2 hours every day.

Seven hours a day? I don’t think even Walt Disney would approve of that.