As the snow fell and fell on Sunday evening, a strange little drama played out in the courtyard of the flats next door. A couple of lads, two of a group that gathered on summer evenings to smoke, drink and film each other fighting on their mobile phones, suddenly sprang out of nowhere, with whoops of joy. They cheerfully exchanged snowballs, traced elaborate patterns in footprints and built half a snowman, before the flurries graduated into a blizzard and drove them away.

Similar scenes could be observed in any one of London's parks yesterday. School was out; transport, too. Here was the gift of an extra day, to be enjoyed in luminous spontaneity and freedom. The heaviest snowfall for a generation allowed everyone from two to 60 a brief sojourn in picture-book childhood.

These days the sight of children, big and small, so conspicuously enjoying themselves out in the open, catches the attention. The invisibility of the conventional family is something that distinguishes Britain from almost every country I have visited in the past five years or so, with the possible exception of the United States.

In Continental Europe you can always see family groups – mother, father and several children, perhaps the dog, too – out enjoying their free time together. I am not drawing the standard contrast here between their genteel café culture and our binge-drinking hoodlums, nor romanticising the enduring Continental custom of Sunday lunch en famille; grand-mère can make everyone's life a misery if she pleases. No, the contrast is between how much time they spend together as families, and how relatively little leisure time many British children spend as part of a complete family group.

Probably it is easy to exaggerate the malaise attached to childhood here, if like me, you live in a city centre. The suburbs are where to go family-spotting. And you could argue that more families are out and about in city parks abroad because more families live in flats and have no gardens. But that's not the whole story, is it?

If you compare Britain with the countries that are our near neighbours, you see more children and young teenagers just hanging around by themselves, without any adult in evidence, and they are out far beyond what you might consider a reasonable bedtime. That group I mentioned do their summer shouting and fighting between midnight and 3am. Not one of them can be more than 16; does no one care, or even wonder, where they are? Apparently not.

And there is now corroboration not only for generalisations like this drawn from personal observation, but for the findings of sundry international studies that place Britain consistently low in leagues of children's happiness. An inquiry conducted for the Children's Society, just published as The Good Childhood, finds that four decades of "excessive individualism" have left this generation of children more troubled than at any time in the past. It blames "aggressive pursuit of personal success" and calls for a profound change in the social value system as the only way to repair the damage.

Now I have a shrewd idea what is going to happen to this report. It will be lionised by traditionalists and moralisers who still dream of a return to the "perfect" nuclear family. Equally vocal liberals will point out that the Children's Society is a Victorian foundation, affiliated to the Church of England – so it would say that, wouldn't it? Its provenance will provide a pretext for the Government to do nothing about it, beyond adding a "parenting class" or two.

Far be it from me to denigrate parenting classes, but the shift in values the report calls for is what should be taken seriously. The difficulty is that so many of the measures taken by this Government have only reinforced attitudes that will make that shift harder.

Generous child tax allowances, long working hours, more day nurseries, the expectation that both parents will work full-time and an emphasis on ambition and personal fulfilment, have fostered a society that imposes scant penalty on single parenthood – sometimes the reverse – and routinely delegates responsibility for its children.

If the real cost attached to bringing children into the world were actually higher, perhaps those children would be valued more. And more love, time and attention would come their way.

m.dejevsky@independent.co.uk