My four-year-old daughter takes my hand, adopts a meaningful expression and gently squeezes my fingers. “I wish your mummy was still alive,” she says.

This sets me on my heels a little, since it has come entirely out of left field. We are walking my son to football training and, up to this point, conversation had been circling the prospect of us all getting ice cream once it finished.

“I know, pet,” I say, buffering slightly, “I do too; she would have loved you very much.” Warming to the theme, my son chimes in. “You can’t really have a complete family without two nanas,” he says. “Well, no,” I reply, “that’s not true – you can have all kinds of families with loads of different combinations of parents or grandparents or siblings.”

He holds my gaze for what seems like an eternity, long enough that I reckon I can see the little cogs behind his eyes processing my wisdom in real time, before tilting his head and asking, with the sincerity of a Trappist monk: “Who’s the best striker in the Bundesliga?”

My daughter is no longer present to see my face set back into its standard factory setting of polite bafflement, since she has ambled ahead of us, my mother’s tragic absence entirely forgotten.

This has been my general experience of speaking to my children about life, death and specifically my own bereavement; brief and abrupt moments of crystalline poignancy scattered at high speed, and punctured by an immediate reversion to cheery indifference. My son’s meditations on grief began when he was roughly his sister’s age, since the philosopher within us seems to take shape at four or five years old. He had, presumably, started doing the sort of mental arithmetic that revealed he was down one nana compared with some of his friends, and would pepper me with questions about this shortfall.

Eventually, conversations like these would teach me the gloriously insensitive patterns of children’s thoughts and reveal that real life rarely adheres to the rhythms of a Very Special Episode of a heartwarming family drama. But I’ll admit the first few times it happened, I steeled myself for the scene I imagined was soon to come: me doling out tender epiphanies to my wise and inquisitive son, scored with soft, swelling music and the sound of his gentle, sniffled tears. And each time, I’d be mildly deflated when my stirring response would be interrupted, about five words in, by him changing the subject to something more interesting like, say, trains or farts.

A lover of maths, he was briefly preoccupied with the idea that all human beings live to be 100 years old. One afternoon, he deployed this grisly calculus to predict the year that he and we, his parents, would die. “Well,” I said, sidestepping his breezy prediction of his own death date, “some people do live that long, but most people die a little before that.”

“Oh yeah! Like your mum!” he said, with a cheeriness fitting the occasion, before turning back to his Play-Doh.

Aside from being extremely funny, I’ve grown to find these exchanges soothing. Last week marked the 35th anniversary of my mother’s passing, and I’ve spent most of my life treating the subject with the tact and poise that society – rightly and thankfully – insists on. The tactful hesitance in speaking about it too much myself, the tiptoe tightrope of apologies and silences it tends to engender in others. Speaking to my children about it, with all their bluntness, candour, even indifference, has been bracing, but also strangely joyous.

[ I routinely have intrusive thoughts about horrible things that could happen to my childrenOpens in new window ]

Of course, somewhere within the innocence of their responses lurks a sharp little ice-pick of sadness; the knowledge that I myself was that same insouciant, carefree child, at precisely the moment my mother died. I’ve tried, over the years, to recall the things people said to me that made sense of any of it, things that could explain an existentially unexplainable thing. Some perfect words to get across that someone, that any of us, could be here one day, and not the next, and that seven-eighths of a life later their loss will still be mourned, but life will still go on.

My daughter returns to hold my hand, my son bringing up the rear. We are quiet now, the three of us. He pats my arm. She squeezes my palm. “Probably Harry Kane,” I tell my son, breaking the silence with the only response that seems appropriate in this moment, “although Patrick Schick at Leverkusen is having a great start to the season.”

[ Séamas O’Reilly: Am I a soft, overprotective dad bringing his own childhood traumas to bear?Opens in new window ]

[ My son’s new hobby is confounding me with ‘mystyrieyos’ riddles that he puts in writingOpens in new window ]