Deborah Orr: Hounded and vilified as a serial homewrecker – who'd be Sienna?

It is difficult to summon a whole heap of sympathy for Sienna Miller. Not so long ago, she was known only as the girlfriend of Jude Law, who started seeing her not long after leaving his wife, actress and fashion designer Sadie Frost, and her four children.

A few years later, and Miller is the bigger film star in her new relationship, once again with a fellow actor, and once again with a man who has recently walked out on his wife, fashion designer Rosetta Millington, and their four children. Will Miller be comfortable with leaving Balthazar Getty with the children and their nanny, as she was, so ill-advisedly, with Law? Not if she isn't stupid.

Except that she does appear to be a little bit stupid, doesn't she? A couple of months ago, when Miller left her last boyfriend, Rhys Ifans, there was some suggestion that she had done so in part because she and Ifans were a "messy" couple, too fond of carousing and partying. This did not play well in Hollywood, and Miller was ultra keen to make it big there.

This theory has been abandoned, now that her affair with millionaire oil heir Getty has emerged. Miller's publicity team is said to be in meltdown, unable to cope with the US-wide hatred that is being flamboyantly rained on its lucrative client. She is now nicknamed, not very hilariously, "Serial Miller" or more baldly, "a home-wrecker". The releases of her two forthcoming films, GI Joe: Rise of the Cobra and Hippy Hippy Shake, have been put back, and despite official denials, it seems obvious that their producers are waiting for the storm to blow out.

Meanwhile, Miller is in a frenzy about the adverse publicity that she is attracting. Earlier this week the 26-year-old became angry and tearful when photographers surrounded her as she filled her car with petrol. She has already taken legal action against The Sun and the News of the World after they published pictures of her "frolicking topless" with Getty. Why shouldn't she? Even a married man who pays prostitutes to whip him during prison role-play is deemed in this country to have a right to some privacy.

Yet Miller does want be in the limelight if it suits her. When she last appeared on the Jonathan Ross show, publicising her film, The Edge of Love, and boasting of her ability to "drink most men under the table", she secured a promise that he would not question her about her own love life. Like many a celeb before her, she is now finding that media manipulation is not as easy as she would like it to be.

Perhaps Miller needs to have a chat with Angelina Jolie, who has moved in a short space of time from husband-stealer to happily married mother of, well, who can keep count? No doubt the two of them would also have a few words to exchange about how it always seems to be the other woman, not the cheating spouse, who gets most blame when a marriage breaks up. So far Getty's career appears undamaged by the abandonment of his wife and four babies. His well-connected wife is said to be gunning not for Getty, but for his girlfriend.

No doubt Miller finds it all too easy to tell herself that she is not responsible for the break-up of another person's family. As for the person who most certainly is responsible, she is sure to believe that he would never do such a thing for anyone else except wonderful her. Anyway, Getty is likely to have gone to great lengths to assure her that the marriage – only eight years old – was over anyway. Miller herself experienced the break-up of her parents when she was five, so there is nothing in her background that might lead her to believe that Getty's children might be suffering anything that cannot be accommodated.

Passion is a powerful motivator, and it is not in Miller's interests to think hard about what her boyfriend is really up to. Getty has spent some years with a woman, who had many babies with him. He has known all of those children from their conception, and has held them since their birth. However privileged their lives are, and however easy it might be to find the money to scoot the children around the world between households, he is still taking a huge gamble on their futures by cutting loose. He is betraying five people, while Miller is merely abetting him.

It is now quite widely acknowledged, to quote Demos director, Richard Reeves, that: "The necessary sacrifices of good parenting collide with the assumption that the individual is entitled to lead his or her life only by reference to their own desires." Miller believes that she is "political", because she likes to rant about the iniquities of the war in Iraq. But the socio-political implications of the mess she's mixed herself up in are deeply important too. She's an intelligent woman and should be able to work that out. Yet it is all much harder for a childless person to understand. That's why it's unfair that Miller is expected to consider the needs of four children far more than their father does, and is being punished because she doesn't. She should be cut a little slack. He's the one who deserves contempt.

These days, children's clothing is a minefield

Widespread liberal mores do, I believe, expose children to explicit sexual messages at too early an age. We are free and easy when it comes to placing sexual material in public arenas to which children have open access, and we should not be.

But I find I cannot join the chorus of disapproval that has been scared up over High School Musical pants for little girls. A concerned mother, Sue Ralph, was appalled to find that an invitation to get into a swimming pool had been printed on a pair of knickers in an Asda multi-pack. Walt Disney, she told the Daily Mail, should have been aware of the double entendre implied in the words "Dive in". The slogan is inappropriate, she says, "because you never know who could be out and about and see that and think it was a bit too enticing for a young child to be wearing".

Apparently organisations including the NSPCC and the National Union of Teachers agree with her. Even Disney agrees with her. The corporation explains that, "a genuine oversight was made" and promises that the product "will not be part of any forthcoming collections".

Let's hear it, I say, for genuine oversight. It is, as usual, the over-sexualisation of adults that is the problem here. Paedophiles do indeed see sexual invitation when there is absolutely none. But it is a little bit sad when organisations that are there to protect children are so keen to emulate them.

* What is this stuff about "collections" anyway? Can't manufacturers just make clothes for children, instead of launching "collections" for them? Traipsing the streets for the dungarees that had become my son's heart's desire, I was told at one unassuming shop after another that "there were no dungarees in their collections this season". I wish we had been informed of this in advance: we could have avoided reading Huckleberry Finn to the child in the midst of what was clearly an inappropriate fashion moment. Thank goodness for charity shops.

* A survey suggests that women start to fret about ageing at 28. What a way to fritter away one's youth. Much better to adopt the view of my friend Eileen, who saw a photograph of herself a decade before, at 35, and was amazed by how much younger she looked. "I decided not to wait another 10 years before marvelling at how young I look right now. This is it. I'm as young as I'll ever be. For ever."