We no longer shield our offspring from the horrors of adult life - they shield us

These have been tense weeks in the Berkmann household. At the end of November, my boy, aged 13, was an inch shorter than me. Right now, as measured in the mirror this morning, we are exactly the same height. Soon, maybe as soon as teatime, he will be taller than me.

I am five foot nine and three-quarters. Or rather, I was at the age of 20. My insistence on the three-quarters and my abject, lifelong failure to reach five foot 10 have long been a source of amusement to the tall blonde woman, who herself is a smidgin over five foot 10, and very pleased about it. For her the shrinkage has yet to begin.

For me, four years older than her and bowed down by decades of gas bills, the future is distinctly shorter. I now weigh in at five foot nine and a half, and I wouldn't be surprised if it's down to nine and a quarter before long, while the boy continues to shoot up like an untethered weed, despite eating little more than Rice Krispies. Not that I'm in competition with him, good lord no. There's no point being in a competition you have already lost.

Actually I'm rather proud of him. The ridiculous, ferocious love you feel for your children supersedes all petty ego-driven issues such as relative height, although I have been saved from this by my daughter, now aged 16, who seems to have settled at a bijou five foot five and a half. For many years she was the tallest in her class and has gradually become one of the shortest. She is also one of the loudest and most opinionated, so I doubt many people mention it to her. But her recent levelling off means that she is clearly the family munchkin, even when she wears her new boots with the giant heels.

I had been preparing myself for that role for several years, and if I shower her with presents now, it's with gratitude that she has taken on the burden so selflessly. In short, I'm pretending that she had a choice in the matter. And in accepting these presents, she is sharing that pretence. Thus begins the inexorable handover of power in a family. We no longer shield them from the horrors of adult life; they start to shield us.

If I am oversensitive on this issue – and I'm not going to pretend I'm not – it's because I myself was tiny as a child, and only achieved average height in my mid-teens, with a last-minute dash over the line. The average then was five foot eight, but in the intervening decades it has crept up. Now most young people are huge towering giraffe-type structures that look vulnerable in high winds. Averages can grow but I can't. British men now are, on average, five foot nine and a half inches tall: soon they'll be five foot 10 and I shall be officially short. Maybe they'll stamp "fun size" on my passport.

My boy, meanwhile, is hoping for six foot and we are egging him on, occasionally trying to feed him food not manufactured by Kellogg's. It is, perhaps, parenthood's most delicate stage, when you realise that these children you have spent all this time and energy nurturing are essentially your replacements.

The newer models, shinier and sleeker in every way, with batteries that stay charged for so much longer. They wear us out, they outgrow us and soon they'll leave us behind, and we love them unreservedly for it. Either we are out of our collective minds, or it's the sanest thing we'll ever do in our lives.