Father and son.

Father and son. Photo: Jessica Shapiro

Couples should not have children if their relationship is not stable enough to merit getting married, a British High Court judge said last week.

Sir Paul Coleridge, speaking out before retirement from a long family law career, challenged the common notion that it makes no difference whether parents cohabit or marry. ''One [arrangement] tends to last and the other doesn't,'' he said, quoting Marriage Foundation research suggesting children with unmarried parents were twice as likely to suffer a family break-up as those with married parents. The proportion of children born to unmarried parents in Britain reached a record 47.5 per cent last year.

Children in cohabiting families lag behind children with married parents in overall socio-emotional and general development. 

When a British authority figure dares to give voice to concerns about this crucial social issue, it makes news because it is so rare. Here in Australia, too, there is deathly silence from our leaders - politicians, social scientists, the clergy, judges - about the increasing casualisation of relationships involving children.

Yet talk to people working with disadvantaged communities and you hear a very different story. They witness the effects on children of being raised in unstable relationships - effects well documented in Australia.

Using data from the Longitudinal Study of Australian Children, Lixia Qu and Ruth Weston, from the Australian Institute of Family Studies, found young families with cohabiting parents were nearly three times more likely to break up than married families. The same researchers showed children in cohabiting families lag behind children with married parents in overall socio-emotional and general development, show poorer learning, more behavioural problems and experience poorer parenting.

Contrary to expectations, it has turned out that children don't provide the glue to keep cohabiting parents together. Marriage - often dismissed as just a piece of paper - does make a difference.

This year, the ''Knot Yet'' report on changing marriage patterns, by the Washington-based Brookings Institution, examined why this was so and suggested the answer may lie in the decision-making process.

Most people marry after a process of discovering mutual commitment to long-term goals. That's often lacking in cohabiting relationships where couples move in together sometimes because a lease runs out, or they are seeking cheaper rent, or it seemed like a good idea at the time.

Families that evolve from these non-decisions are, unsurprisingly, far less stable. The non-decisions apply also to child-bearing - the Brookings report notes the high incidence of unplanned pregnancy in these arrangements, with half of births to unmarried 20-something women ''unintended''.

The result, according to the report, is a growing social divide, with well-educated people still tending to marry and then have children, while lower socio-economic groups are more likely to have children in de facto relationships. These children often end up in single-parent families. This emerging difference in marriage patterns is adding to the gap between the haves and have-nots, increasing social disadvantage.

Of course there are de facto couples with lasting relationships and thriving children, but the broader patterns tell a different story - just as the 90-year-old who smokes has no bearing on the link between cigarettes and health risks.

Pope Francis recently announced he was surveying all Catholics about family life. His questionnaire, which seeks response from clergy, Catholic organisations and parishioners, expresses concern about social changes, including ''the widespread practice of cohabitation'', and asks about the prevalence of such couples in Catholic communities and problems with pastoral care in these circumstances.

Responses will be interesting, given that 40 years ago clergy readily spoke out about the benefits of marriage, whereas these days few dare raise the ''M'' question for fear of ostracising their shrinking pool of parishioners and attracting unfavourable media attention.

The media is part of the problem, given in their number are more than a fair share of cohabiting couples. For instance, the ABC is full of well-educated presenters and producers bucking social trends by successfully raising children in stable de facto relationships or single-parent families. They naturally resist any public discussion of their choices.

One example is Richard Glover, from ABC Sydney, who boasts of his long-lasting de facto relationship. He has publicly taken issue with my reporting of research on this subject. ''Do our children miss out on anything?'' he wrote. ''Well, yes, Bettina … Principally, I think, they miss out on vases,'' he said, of his family's lack of expensive crystal vases commonly given as wedding presents.

Public discussion of this important social trend is discouraged by media players who won't acknowledge that their preferred lifestyle choices have very different consequences on the other side of the social divide - yet the impact on kids of the casualisation of family relations is no laughing matter.

Bettina Arndt is a social commentator.