I knew it was only a matter of time before one of my daughters asked: “Does my bum look big in this?”

I thought it would be the 16-year-old, who spends half her life in front of the mirror moaning about everything from her toes to he teeth. But it was her sister, two years younger, who asked what is probably the most asked question of womankind.

“I love it, but I think I look wide,” she said, craning her neck to inspect a new top.

Teenage girls are obsessed with body image. They are forever comparing themselves with others, most of whom they believe are prettier than they are, or have a better figure.

I can see how too much of a fixation could get out of hand and cause problems, but it’s hard to find ways to reassure them when the whole of society seems obsessed with it too.

In a world which holds an appreciation day for Pippa Middleton’s rear and sticks videos entitled ‘When Kerry Katona Got Fat’ on YouTube, how are we to convince our children that it is okay to be bigger than size six.

My eldest daughter was insulted when I suggested she try on a size 10 dress in a shop. The six was clearly too small, but she wouldn’t have it.

I don’t remember being so bothered about my weight at her age. Obviously, I didn’t want to balloon to enormous proportions, but I’m sure I wasn’t tempted to throw myself under a bus when I graduated from an eight to a 10. But now, according to a survey, girls as young as ten worry about their weight.

I’m tired of reassuring my daughters as to how slim and attractive they are because it falls on deaf ears. My youngest daughter refused to get out of the car to help me shop the other day because she had on a pair of baggy joggers rather than skin-tight jeans. It was Asda, for heaven’s sake, not Prada.

I look back with sadness at the times when they would happily pull on just about anything I gave them and not even glance in a mirror before leaving the house.

How things have changed. Now they spend so long scrutinising legs, bums and tums, you’d think we had a wall of paparazzi waiting outside. I keep asking them who they’re trying to impress.

I blame glossy mags – they’re into Vogue at present (bought with their own money, I might add) – and TV. Or maybe they just don’t want to turn into me – because my bum looks big in most things.