When I get up in the morning, the first thing I often do is switch on the radio to catch up with the news.

It's part of my morning routine, something to listen to with half an ear while I get the breakfast.

But these days, as my hand touches that switch, in the moment before the radio flicks into life, I find myself holding my breath. For just the smallest fraction of time - a tiny part of a second, that's all - my heart thuds. I'm afraid, even bracing myself for... what?

I move the switch. The voice of the newsreader fills the room. His or her voice sounds completely normal, the calm level tones that greet me every morning. He (or she) is talking about some tedious political argument; some new revelation of dubious goings-on in government; the latest batch of statistics, perhaps a robbery or a murder. All the things that fill the news every day.

The tiny anxious moment is over. It's all right. I can relax and go on with my life as usual. Today at least there's not been an explosion in London, a release of poison gas on the Underground, a suicide bomber on a London bus. Our son and daughter, their partners and our grandchildren are safe, at least as far as terrorist threats are concerned.

It's silly of me, perhaps. But I know I'm not alone in this. I know other mothers whose children live and work in London, and they too have that little niggling fear always in their minds. It's not that we're obsessed by it. It doesn't stop us getting on with our lives. Most of the time we don't even give it a thought.

But it's there at the back of our minds. And each day that the news tells of other things, each day that we don't switch on to find an extended news bulletin with everyone talking in those special solemn voices they reserve for such occasions, each normal day, is a bonus.

It's partly, of course, that mothers never quite stop worrying about their children, even when they've grown up and left home. And, of course, there are lots of other things that could harm our distant families, small things that never make the news but can rock family life to its foundations, turn your world upside down in a moment. The newsworthy things, the big threats, are just an added dimension, an extra anxiety.

Sometimes as I sigh with relief I'm taking in news of an atrocity on the other side of the world: an earthquake in the Far East, floods and hurricanes; suicide bombers in Israel or Iraq. They're bad things, but they're far from home.

But for some people they're not far from home at all. There are mothers listening whose sons and daughters are serving in the army or spending that gap year backpacking far away. For them, today, there may be no sigh of relief.

Whenever, wherever, someone is killed, whether by natural disaster or terrorist action, there are families left grieving. Every time news comes of the deaths of one person or of thousands, someone, somewhere is facing the reality of their worst nightmare taking shape.

And if I worry like this because my children are in London, how much worse must it be for those whose families live or work in the world's true trouble spots, who really have cause to catch their breath as they turn the radio on for the news?