Lisa Markwell: When girls dress like this, are they not just trying to be more like mum?

Materialism is one thing, wanting to appear sexually available quite another

Was it when my ten year old daughter said her most-wanted Christmas present was "a bra" that alarm bells started ringing? Or when she took to singing "Doncha wish your girlfriend was hot like me"? The oft-lamented "sexualisation" of children became a political buzz-word again yesterday, when David Cameron appeared on Radio 4's Woman's Hour claiming the Tories would crack down on the push-up bras, "Lolita" bedlinen and so on that have been marketed at children in recent years.

We've heard all this "let's protect the children" before – from Ed Balls claiming victory over advertisers of fast food to Esther Rantzen establishing ChildLine (she later worried that she'd created over-meddlesome child-protection officers).

Lily Allen's sing-song delivery disguises lyrics about a sexually incompetent partner; Katy Perry, we now all know, dabbled with lipstick lesbianism. Tweenagers copying the dance moves they see on TV talent shows resemble auditionees for lap-dancing clubs. Children want to be like these stars – they are, y'know, impressionable.

When Katie Price puts two-year-old daughter Princess in false eyelashes and posts a video on YouTube, or Tom Cruise's little Suri, just three, appears before the world's paparazzi in lipstick, heels and a designer handbag, we might howl, but are they just giving in to their children's pestering to be more like mummy?

The answer can't be for mothers to dress in Amish modesty (although perhaps laying off the PVC corsets and stripper heels around the house might be an idea, Jordan); sexual imagery is hardly a new phenomenon. It is the invidious acceptance of this stuff as standard issue reality, rather than risqué marketing, that should worry all of us.

Some of the power lies within the purse. We can shun the push-up bras and flimsy knickers marketed at children, and deny the Cyrus family – who have already inflicted the sexually precocious Miley upon us – any sales of the fishnet tights and heeled boots fashion range being flogged by little sister Noah. Just ten, she poses for the cameras with hip jutted forward and a faintly come-hither stare she didn't learn in school. Penny Nicholls, director of children and young people at the Children's Society, states that parents are reporting children's anxiety about keeping up with trends, and that they are "more materialistic" than in the past. We must ask ourselves, as we talk of must-have handbags and upgrading the plasma screen, whose fault is that?

We can demand that the Advertising Standards Agency get tough all we like, but they are not the only villains of this piece. Materialistic is one thing, wanting to appear sexually available before puberty is quite another. And it is less in the actual bras and pillows that the danger lies; these items are, after all, bought by mums and dads, not the children themselves. It's the drip-drip-drip of Lily's lyrics, Miley's tattoos and Cheryl's dance moves.

David Cameron answered his own question when he went on to explain to Jenni Murray how his daughter Nancy was stopped from listening to Lily Allen's songs – his wife wrestled the iPod away from her. We haven't got time to wait around for a policy, we must be prepared to factor vigilance and cool headed explanations of sexual appropriateness into our parenting skills. It may make us squirm to explain to our daughters what a prostitute is and why it's not a good idea to dress like one, but it's clearly, sadly, a necessary embarrassment.