Being an auntie is a pretty good gig.

In fact, dare I say it, it even has some advantages over parenthood. You are practically required to provide sweets, even if mum's idea of a treat is a carrot baton. You're spared the drudgery of getting the children fed and ready for bed, but get all the glory of reading the bedtime story. Aunties get to relive their own childhood playing boisterous games but can slink off quietly when someone starts bawling. Fun is for aunties, in other words, but discipline is for parents.

According to parenting author Steve Biddulph, however, there's more to aunties than that. Fifteen years ago, Biddulph published Raising Boys, which struck a chord with anxious parents and sold four million copies. Now he has written Raising Girls, and this time advocates an "aunties' army" to help steer young women through the choppy waters of adolescence.

Girls today, he warns, are in a state of crisis, relentlessly besieged by toxic messages from advertising and television, pushing them to be perfect in every way. Aunts, says Biddulph, ought to be taking a more active role in their nieces' lives for those occasions when a girl isn't getting on with her mother or needs to talk about something she feels awkward about raising with her mum.

It's true, aunts are important. They represent to children the mystique of adulthood in a way that parents, being so close, cannot. They can offer a sensible, ironic, reassuring perspective to counterbalance the nonsense children pick up from each other and the media environment, and help girls stay grounded.

Why stop at aunts, though? Surely it's extended family as a whole – aunties, uncles, grandparents and cousins, not to mention close family friends – who help provide children with an alternative perspective. For thousands of generations, humans lived in close proximity with their extended families; it is only really in the last century, and particularly in the last 50 years, that people in the Western world have been living in such huge numbers in atomised nuclear families or, increasingly, as couples or single people, often far from their parents and siblings. Government figures in 2010 showed that more people were living alone and more children being raised by single parents than ever before. A de facto segregation of the generations, with the elderly living alone and in care homes and having only occasional contact with the young, has intensified the process. What do children lose from knowing fewer adults well? A range of authoritative voices in their lives, voices that counterbalance those directed at them though marketing and television.

So greater contact between children and their extended families would most likely benefit children. What is now required, however, is a definition of family that doesn't merely hark back to a 1950s ideal. The beatification by right-leaning policy-makers of mummy, daddy and child, with aunts, uncles and grandparents in the background, bathed in their reflective glory like shepherds in a nativity scene, is unhelpful in an age when only around a third of adults are living in homes with children (compared to more than half in 1961), many of them single parents, and many living miles from their own parents and siblings.

No wonder "family" has taken on a new meaning. "My friends are my family," is a widespread sentiment. The role of godparents has taken on renewed importance as people with children turn to their loved and trusted friends to provide a guiding role in their children's lives. One friend of mine, who has no children, takes her role as godparent so seriously that she spends at least a weekend a month with her godchild, his siblings and their mother, even though they live a two-hour drive away. She is there for birthdays and even Christmas. The whole family adores her.

We can wrack ourselves with grief over the tragic breakdown of the traditional family, or we can move on and embrace this new reality, where being an "aunt" or "uncle" often has nothing to do with being a blood relative, but has everything to do with taking responsibility for the wellbeing of the next generation. We appear to be resurrecting the role of extended family, but with a much broader definition of the term. That has to be good for everyone.