You really do go round in circles. You don't go fast. And you certainly don't go far. When you take a child out on a run, there's nothing to show at the end of it, no cake baked, no mind-expanding book read, no museum ticked off the list. But running with children is a revelation. Unlike most "kids' activities" – surely words to make the most maternal of hearts sink – it's free, and it makes you feel free. It doesn't involve noise or crowds or changing rooms. It lifts the spirits, and the bottom. And, as I discovered, it brings you closer to your children in unexpected ways.
I'm really not a runner. I do not have PBs (personal bests) not referring to cocktail consumption. Neither do I own any expensive equipment that measures heart rates or pace or time. I don't subscribe to any running magazines, even if I do occasionally flip through my husband's copies for the recipes. (Yes, my husband is a proper runner, and a whippet-fast one.) Even the word run is slightly misleading in my case: I propel myself forward at a slightly faster pace than a smart walk.
Built for pleasure rather than speed, I only started running a few years ago on the persuasion of a friend who fancied some company plodding around our local park: she was trying to lose weight in time for the Christmas parties (she was talking my language). She knocked on the front door twice a week, marched me down to the park. We'd loop it a couple of times, bundled up in scarves and gloves, gossiping and panting. Then my friend got pregnant and decided to nest.
But it was too late for me. Not only had I discovered that if I ran regularly I could eat more cake without putting on weight, it was obvious that running helped counteract my generally unhealthy life – crouched over a desk indoors, over-caffeinated, tweeting – in a far more bracing way than the gentler arts of yoga and pilates. I discovered something pleasurably punishing in running alone: gruelling and a bit lonely but satisfying. So I persevered, viewing it as a constitutional.
All this changed one afternoon about two years ago when I took my elder son, Oscar, then eight, running with me. It was a spontaneous act of desperation on a day when the warrior screeches from my living room echoed down our street. It had rained all morning. Cooped up, the children were fighting and disembowelling the sofa. They needed to be out.
Yes, the cliche is true, boys are like dogs – loving, loyal, always hungry and in need of daily exercise. Unless you have a big garden, you're stuck with a grim schedule of bone-cold swimming pools, muddy parks and football matches. You can, of course, just hand them the TV remote or wire them into an Xbox, but it won't tire them out. And it won't fulfil that basic child's need: to run. Try it, they're like greyhounds released from the box.
I loved that first run with Oscar, as I've loved every run with him since. With him beside me – grinning but a bit self-conscious, desperately hoping he didn't bump into any mates from school – I forgot to find running gruelling. I even forgot that I was slow: while my husband would be frustrated at our pace, Oscar and I were well matched, quickly falling into the same rhythm. I've never come back from a cold park with wet feet so exhilarated and happy. Unexpectedly bonding in a we-did-it kind of way, it made me realise how little sport – using the term loosely – with the boys I participated in. So much of it has fallen into their dad's camp over the years. Running is a way I can get physical with the boys. And, more than any other activity, it's the one that bonds us.
Sometimes Oscar and I run in cheerful silence. But mostly we chat: I've never had more intimate conversations with Oscar than when we run: his worries, his dreams, black holes, Percy Jackson novels, the best Haribo of all time – all the big stuff. Without direct eye contact – at most, it's a sideways glance – and with the focus on the physical, my son is somehow more free to express himself, both the focus of my attention and peripheral to it. It's one of the times when boys will be more open and vocal – when they are doing something else. It takes the pressure off.
In motion, in the fresh air, all that direct, interrogative questioning – "Have you done your homework?", "Who painted the sofa with toothpaste?" – is left in the house. There is no competition – from siblings, the laptop, box sets – for my attention. No goals to score. No peers to impress. When you run, the mind is free to wander.
As the months have gone on, Oscar, nearly 10 now, has got fitter, faster, taller, and, pace-wise, has to humour me on his long, springy, coltish legs. We're pretty much the same trainer size. He's discovered that he's a naturally talented runner, like his dad, but also that the more effort he puts in, the better he gets: a valuable life lesson learned rather than spelled out in a classroom. Soon he'll have outpaced me completely and his dad will have to take him running because I won't be able to keep up. Nonetheless, I've also got fitter and faster, mostly because our runs have become longer, more adventurous. Since we moved out of London, it's less about looping the park than running along canal towpaths, renaming the canal boats, and sniffing the smoke spiralling from the wood burner chimneys.
If it all sounds a bit idyllic, well, it is actually. It's ace. My six-year-old son, Jago, also wants to run now because he wants what his big brother has. I take him out, like Oscar, on his own: it seems to be the one-on-one element that the boys thrive on. The runs with my younger son involve rather more slapstick tumbles, treading in dog mess and stopping to inspect butterflies, but they're a lot of fun – he runs with a beaming smile on his face – and he is always puffed with pride by the end of it. I'll take my four-year-old daughter out on her own when she's a bit older too.
Now that I take my boys running – once a week, each boy – I can't understand why running with kids is not more popular. I don't see many other children running with their parents – a lucky few, we smile in acknowledgment of one another – although I do see lots of people running with their dogs, which suggests that the dogs are the ones having all the fun outside. I say, seize the opportunity to run with your kids if you can, while you can: it's a small window. Sooner or later, they'll outrun you anyway, find your pace frustrating, your sweaty gear and nose-panting embarrassing. They'll discover Facebook. Get them young and they might still be running when they're old. Just like you.
• Polly Williams' new novel, Husband, Missing, is published by Headline, £6.99. To order a copy for £5.59 with free UK p&p go to guardian.co.uk/bookshop or call 0330 333 6846
Follow Polly on Twitter @pollywilliams