It could be any Saturday night, almost certainly the wrong side of 9pm, and our two elder children – 11 and 10 – are settling down with us to watch a "family film". It's a weekend ritual that we initially encouraged as a shared alternative to screen-time but has now somehow created a different kind of problem.

"OK, so two episodes of Modern Family, says one, stretching out on the sofa.

"Yup, and then my choice on Netflix," continues the other. "And, er, Dad, where's the homemade popcorn you promised? Not too much salt this time." Endless snacks and a luxury of viewing time lies ahead of them, and we are consigned to refreshment duties, trips back and forth to the kitchen for the next round. Oh well, there's no more sofa space left for us anyway.

When we're lucky, we get an hour or two alone, but it's only temporary. Often we have to keep the television volume down low, knowing certain shows, like a beacon, will draw them back downstairs, indignant and slightly hurt. "I can't believe you're watching this without me!"

"Breaking Bad? What's that about, a chemistry teacher? So why's it unsuitable for children then?" Our three year old, blissfully, has yet to discover a world beyond CBeebies' Sarah & Duck and bed at 7.30pm, but we're living on borrowed time.

I'm increasingly reluctant to admit how long my children stay up: "10pm-ish, er, quite often," I confess to a friend.

"Oh God, yes," she replies. "All the time. At least when he was a baby, I could Gina Ford him and our evenings were our own. Now he sulks when he's not part of whatever we're doing."

Welcome to child-centric family life where time alone has all but vanished. Adult recreation – supper, a glass of wine and Newsnight – now merges amorphously with last-minute maths revision, packing sports kits and urging children to get ready for bed – a ritual they are true masters at protracting.

Couples therapists would say parents like us should work harder to balance our priorities in order to preserve the family unit. It's even on the political agenda in some countries; well, Scandinavia anyway. Last October, the government in Oslo issued a plea to parents in Norway to embrace "date nights" more frequently in response to rising divorce rates – now 40%, with those aged 40 to 44 most vulnerable to separation.

It has always struck me as a fatal flaw in Darwinian logic that the institution most essential to a child's wellbeing – the couple unit – is the very one they are most likely to, unwittingly, sabotage and undermine. Marital therapists will tell you that one of the times a relationship is most at threat is during the first year after the first child is born.

Emma Cook and her husband, Simon, before their children came along.

Our relationship is strong but it was the arrival of No 3 that made me realise how in need we were of child-free time together. While most of our friends were enjoying the freedom that comes with children reaching secondary-school age, we'd gone back to the beginning with a small baby. Only this time we were older, more exhausted and, crucially, outnumbered. If we did go out, it was often separately to save on babysitting costs. The one recommendation that came up again and again, from friends and experts in the field, was date night. Scheduled time away from the children, however un-spontaneous is, they said, essential. "Stand up to your children," advises Professor Janet Reibstein, a psychotherapist and author. "If you can't put yourself first sometimes, it is the slow death of a relationship." Point taken.

Yet date night wasn't a concept I warmed to, as it sounded over-prescriptive and trite, in fact rather similar to its cliched relative Valentine's Day. I could see that the idea behind this was less commercial but I worried that it felt too forced, sitting in our local pub two streets away for no particular reason other than to escape our kids.

There was also a mounting sense of pressure – as in, we're paying the babysitter £30, so this had better be good. Our first foray into date night ended with an argument in a cab home about some child-related minutiae, the very subject we were meant to be escaping. Still, it was freedom in itself to be out of the house openly debating and discussing all sorts of issues in-depth without fear of a small child over-hearing or hijacking our conversation.

Six months later and date night is still something we commit to once a month. Meanwhile, the exercise itself has inspired more imaginative ways of being together. We now plan regular days off including on birthdays and anniversaries, taking it in turns to organise a day of cinema, art galleries and lunches. Long lunches, we've found, are often more enjoyable than contrived evenings, maybe because they feel more illicit and stolen.

It's still a battle to preserve that time alone. Often the children will text or try to contact us, asking us where we are and what time we'll be back. That is why we would never risk a "date" at home – it would immediately be sabotaged.

The hope is that the odd night off should unite us once we face the battleground at home. On the whole we have been happy to let our kids colonise our company with the military efficiency of an army, advancing on small continents of time that we used to cherish. But it can be frustrating too. Any serious or gossipy grown-up conversation that they used to ignore as smaller children is now monitored, challenged, interrupted.

When I was growing up, I was more of a listener at the door, sitting quietly on the stairs. I would eavesdrop discreetly on my parents' conversations and what they were watching on TV but I would never assert my right to be there as my own children do.

In many ways I like the fact they are more confident, actively challenging, and shaping, family conversation. But that brings new challenges. They are quick to pick up on the few exchanges that don't involve them: "I can hear what you're talking to Dad about", "What are you saying about our auntie's memory?", "Why are you whispering?"

I know this is a situation of our own making and I do sometimes wonder how the balance of power has tipped so far in their favour, and so quickly. I'm sure it started from good intentions. We delight in having our children around, sharing the things we love doing with them.

If we're overly involved, it's only because we're conforming to what is expected of parents these days, which is a daunting amount. Our own parents' generation, particularly fathers, didn't take nearly such an active role; helping with homework, reading and encouraging them to read aloud too, organising their social lives, talking through emotional issues. All that simply wasn't required; somehow it wasn't necessary as it is now.

Every parents' evening I attend encourages a high level of participation in their studies, listening to them practise piano, reading to them and encouraging them to read aloud, completing an art project, much of which often begins when I'm back from work; part of the reason they go to bed later. Even when we're not around, we're available to them via FaceTime, text and email.

That is why parent-and-child experience is so much more enmeshed and inevitably it's much harder to draw the line. The old boundaries don't exist as they did in the days when wives were expected to put their husbands first in the family pecking order, anxious that they shouldn't grow envious of attention diverted to the children. The consequence of all this is increasing anxiety about the quality of time, if any, that couples spend with one another and the long-term effects on family life.

Every relationship expert places time together high on their list as the cornerstone of a thriving relationship. Reibstein, author of The Best Kept Secret, spoke to hundreds of couples to find out what made relationships endure. "All the successful ones preserve time together," she says. "One couple had six children but always made it to their local pub each week, throughout their lives, and that's why they were able to carry on enjoying each other."

Relationship therapist Andrew G Marshall outlined in his book I Love You But You Always Put Me Last, rules on how over-indulgent parents should "childproof" their marriage, including locking their bedroom door at night. This seemed a little harsh but his central point was valid, that couples who rarely have time away from their kids are storing up problems for the future.

In a few years, when they reach adolescence, I know that my children will probably want us as far away as possible but, for this brief period, it's a case of stealing time when you can. My friend and her husband leave her pre-teen children at home each Saturday morning and go to a cafe nearby for breakfast. "Even going to a supermarket without them is fun because it feels like a novelty, it's grownup time."

Linda Blair, a clinical psychologist and author of The Key To Calm, says one couple she worked with could just about afford a babysitter but nothing more. "They found an alternative – driving around in their car for a few hours each week. It really improved their relationship."

Expense isn't a sufficient excuse says the psychotherapist Philippa Perry. "You can always do something that doesn't involve money. Go for a long walk with your partner, which is what I do every weekend. It can be better than a drink or a meal because it's free, it's less distracting, you're doing something and it's more intimate and conducive to sharing."

Of course, the most important aspect of carving out time away from our children is showing them that there is, and should be, life beyond the family. They need to know that, and follow by our example, in order to grow away from us and become independent too. "You've got to make sure your children know that being a grownup is fun in its own right," says Blair. "We tend to dote and wait on them too much, and the message they get is, 'When you grow up life is all about serving the generation beneath you.'" With popcorn late into Saturday night if you're not careful.