It feels like about 13 minutes since I became a mother but tomorrow my third child, my baby, turns 20. And just like that, there are no teenagers in the family.

From the time they were born, I was under no illusions they wouldn’t always be tiny screaming oranges in fright wigs. All things being equal, they would grow up and leave.

Their parents’ role, I would intone sensibly, was to give them the tools and love to make them independent and useful enough to be out in the world.

It was the point and ultimately the end result of the nightly family dinners, the hideous 4.45am drop-offs at the rowing sheds, the school fees. I was down with it.

What I didn’t know was the hollowness and confusion left when the job is done.

People keep saying, ‘It’s time for you now.’ Sorry, what does that even mean? Raising kids always felt like the best me-time ever. I laughed for decades. Now I’m not sure I even know how to be without the gorgeous responsibility of them.

There’s weird anxiety. Yes, they’re armed with degrees, handyman skills, can all drive manual cars, ski, tear it up on the dance floor and make cocktails. But do they know the critical point to add the sugar into the egg whites when making meringue? How to clean a shower? What ‘lounge suit’ means on an invitation? Do they even know how to address an envelope?

Before and after: School drop-offs end just as soon as they started.

Things I miss about being a hands-on mum: Friday night Mario Kart tournaments. Pokemon cards. The glorious Lord of the Rings marathons where everyone wore Middle Earth getups and my dressing gown was roped in as Gandalf’s robe. Road trips in our mini bus (called The Bosom of Abraham), all of us belting out Tiny Dancer.

I miss Uno and Monopoly games in the caravan. My girl wearing her Dorothy costume made by Grannie for her entire time at three-year-old kinder. The familiar dear little face in the pack of kids singing We Are Australian.

I miss one son’s daily line as he opened the car door at the train station after school: “What’s for dinner?” The sleepy Sunday morning faces and arguments over lunchboxes left in school bags. I miss smoothing my girl’s hair into a ponytail and tying in her white ribbon.

There were awful days. The obscene white gleam of bone from a broken 10-year-old arm on a tennis court, courtesy of a too-wide backhand. Post-party vomiting from a top bunk. The flat voice across the desk of a police sergeant: “Don’t be a smart arse, son.”

Kate Halfpenny with her kids and husband in 2004 (top) and 2017 (bottom).

A towering boy burying his head in my shoulder and weeping as his father shouldered the coffin of a beloved family friend.

Seeing a motionless 15-year-old  prone in the rugby field mud and ticking off heads with increasing anxiety. Not him, not him … where’s the bright blonde one? Sudden silence. Other mothers’ faces turning: “It’s Felix.”

Their father and I urged them to move out of home early, telling our own stories of living on beer and cheese on toast in share houses. So they did, blithely peeling off at 18 or 19 in cars stuffed with what for them were just essentials – favourite childhood linen, cricket bags – and for me were the measure of our lives together.

When the oldest left for university in Sydney five days after blowing out his 18 candles, I took to my bed like a Victorian great aunt.

Second time was just as hard. Finding our son’s R.W. Williams’ brown Craftsmen left behind in the wardrobe had me curled and sobbing on the floor, remembering him clomping in his first tiny boots at age two.

The third, my beautiful girl, was the killer. I stood on the Saturday morning footpath and waved her off, smiling reassuringly like the biggest fake of all time. Then I nearly had to go to hospital. I felt like a rat was eating my heart.

The incredibly lucky thing is they’re all happy and healthy and can come home for dinner anytime, but it doesn’t solve the constant mental niggle that I’ve forgotten something. Like, what is meaningful to do with my time. And that there’s nobody to eat the weekly chocolate cake so I can probably stop making it.

Fingers crossed they similarly take to heart the other advice hammered home over the years: don’t wait to have children. Best thing ever.