In the early days of my tenancy of this space, I wrote frequently about my young son. I wrote about his departure to boarding school, aged 8½, a memory that still haunts me, although the experience left him remarkably unscarred. I wrote about the prolonged terror of Common Entrance and his arrival at Harrow, the fifth generation of Carlisle sons to go to the school on the hill (but perhaps the first to arrive with a goose-down duvet). I even wrote of his longing to read History at Oxford, but I’m not sure if I followed up that story. He’s just finished his third year at Edinburgh, where he’s reading Theology.

In those olden days, we had a deal. If I mentioned Sam in a column, I paid him £1. As he rarely read Country Life (his allegiance has always been to The Field), payment was on the honour system. By the time he reached 21, I reckon I had mined the purest veins of this precious lode. I was tempted to write about his 21st-a dinner for 60 friends, followed by Scottish reeling in the barn and a dawn swim in Lake Bofus. Everyone slept in the house, which looked like a refuge from a disaster, but, as we always hope to say after family reunions in the South, ‘nobody got hurt’. I didn’t feature it, however, because, at age 21, one’s children claim a statute of limitations.

But, as with all vows of silence, the urge to blurt out occasionally wins. Five days in New York City with the 22-year-old Sam make the discreet restraint of motherhood impossible. We converged in New York after I’d spent the week in Maine and Sam had spent a week fishing the rivers in Hampshire, tracing the steps of Izaak Walton. Although we weren’t staying together-he was staying with friends on the Upper West Side, I was on the East Side-the plan was for him to show me ‘his’ New York. I introduced him to the city during an autumn half-term when he was 14. He now knows it better than I do.

I think it’s called a defining moment. After nearly two decades of being in charge, I surrendered to the grown-up child. The only vows I kept: no remarks about the beard that has transformed my smooth-cheeked boy into a Norwegian lumberjack and no comments when he orders a cocktail while studying the menu. He planned the days, booked the tables-I followed (and paid). We had dinner at The Modern at the Museum of Modern Art, were spellbound by the Alexander McQueen exhibition at the Met.

We ate lunch at the very cool Breslin in the Hotel Ace on West 29th Street (the world’s best Caesar salad), drank iced coffee at Stumptown Coffee Roasters and walked to the Gagosian Gallery on West 21st Street. A perfect space, peaceful (and free), we both loved its exhibition of Picasso’s paintings, drawings and sculpture of his most enduring passion, Marie Thérèse. It’s a show that won’t be bettered in my lifetime.

Next to the gallery, up two flights of metal stairs, Sam led me to another thrill: High Line, the elevated freight railway built in the 1930s to carry meat carcasses into the city. Its last journey of frozen turkeys was in 1980, and it came close to being demolished, but, thanks to the vision and determination of a handful of landscape architects, it was transformed into a public park, an oasis of trees, shrubs and grasses above the city. The day before, the second section had opened, including the first stretch of lawn on the High Line, lush green grass to walk on barefoot (no dogs are allowed in the park). It is the closest proof I’ve seen for the idea that the Big Society could change the world.

Meanwhile, my world has changed. The boy who baulked at cultural outings is now like the sorcerer’s apprentice, with unseen powers to reveal a whole new world to his mama. For this, I owe more than a quid.

* Subscribe to Country Life and save 40%