"I'VE seen the Eiffel Tower!" That's Jonah's boast at nursery, ever since our family trip to Paris. He's very proud of this achievement, if only because he really was hugely impressed by the famous landmark.

On the other hand, don't we all have the occasional urge to go in for a bit of one-upmanship? Jonah is as pleased as any of us would be to have something special to brag about. We all do it, of course. It's a natural instinct, and it starts young. In our family, there's a story about my uncle Rob, now long dead, who as a six-year-old, spent a summer holiday in the company of a boy whose parents lived - rather grandly - in India, when it was still part of the British Empire. "My father killed a tiger!" bragged this child of the Raj, full of news from 'home'.

In those days, killing wild animals was something to be proud of. My uncle Rob thought very hard for a moment. How to go one better than this one, or at least equal it? His father - my grandfather - was a mere civil engineer, living in an ordinary house in England far away from tigers and other exotic and dangerous animals. Then inspiration struck. His father did, after all, have battles of his own to fight against undesirable creatures. Rob's face lit up. "My Daddy killed a slug!" he crowed.

As you get older, you learn that if you can't go one better you can at least try to deflate the pretensions of the person who's boasting. Like the secondary school child from County Durham on a trip to France, whose party shared a lift in the Eiffel Tower with three American tourists who were obviously trying to impress with a long list of all the places in Europe they'd visited. They clearly believed they'd done it all. When at last there was a gap in the talk, the child piped up: "But have you been to Ushaw Moor?" I do rather doubt that the Americans went home feeling crushed, knowing that they'd missed this essential tourist hotspot from their itinerary. But it was a good try.

As for the family legend about my uncle Rob, when I think of it now, I add my own bit of one-upmanship. My boast is that grandson Jonah likes slugs; he finds them fascinating; he's a lovely caring child who wouldn't willingly hurt any living creature. You see, I'm doing it too. But then we grandmothers are probably the very worst offenders when it comes to boasting.

Parents are bad enough. We've all heard them, the mothers whose little darlings are just the most intelligent children ever born, their bad behaviour due only to the failure of the world around them to acknowledge that intelligence and channel it in a constructive manner. In fact, many of us have been those parents, in our younger days. But now we're grandmothers, we have absolutely no doubt at all that our grandchildren are the most delightful children this world has ever known. Their little sayings are funnier, more heart-warming, than those of any other toddler learning to talk. They smile more brightly, hug more lovingly, look more charming, than anyone else's grandchildren.

During our last visit to the family in London, a passing American tourist paused to gaze at baby Theo and gushed to his companion: "Isn't that just the most sweet baby?" Who am I to disagree? He was only saying what was blindingly obvious. As for Jonah, when people say how gorgeous he is, comment on his smile or his good behaviour, laugh at his funny remarks, I look on all this as his due. He's my grandson. He's perfect, even when he's naughty.

Unlike most grandmothers, I've been fortunate enough to be able to boast about him in public, through these columns. I've loved being able to share my feelings with you all. But the trouble with proud, boastful grandmothers is that they can get very boring. They're so full of love for their grandchildren that - given half a chance - they go on and on about it. They start repeating themselves, endlessly. I don't want that to happen, so I feel the time has come for Gran at Large to take a final bow. But though she won't be around in this space any more, I expect she'll somehow be back now and then to boast about the things the boys have said or done, to share her delight in these special people. After all, I'm a grandmother. And isn't that what grandmothers do?

* Mother of five boys, Ruth Campbell writes a new fortnightly Mum at Large column in this space in two weeks' time. Look out for Helen Cannam's new weekly column on the opposite page from May 12.