I have an old (some would say very old) school photograph, taken when I was in my first year at secondary school.

There are 400 boys and around 30 schoolteachers in it, in five rows, with the younger boys sitting cross-legged on the ground, and the older ones sitting and standing behind them.

I take that photograph to primary schools today, when I'm asked to talk about health to them. We chat for a while, then I bring it out and ask the boys and girls what they notice about the children in the photograph.

They never give the obvious answer. They comment on the curious clothes and haircuts, and the fact that there are no girls, and that it's black and white. They don't notice at all that there isn't a single fat child (or for that matter, teacher) in the whole picture.

It's not only that in the photograph the children aren't fat - they all look considerably thinner than even the average children of today, who would now never be considered as overweight.

When today's children look at that photograph I hear remarks like they must have been starved' or did they never get anything to eat?' It's then that I go on to discuss with the children how we spent our days. No-one came to school by car - most of us walked or cycled. There were 350 cycle parking spaces in the playground, and they were all filled.

We cycled through the normal rush-hour traffic, and didn't think anything of it. We all stayed for school dinners, which involved meat and two veg followed by fruit and pudding. We hadn't heard of junk food, and we simply supposed that everyone ate like we did.

However, the point I'm making isn't about how good the old days were - far from it. Things are much better now. We have many more choices about what we can eat and how we spend our lives, and if we can counter the pressures put upon our children to eat unhealthily we may be able to reverse the trend towards increasing obesity in children. If we really achieve this, we will avoid a lot of trouble in our next generation of middle-aged adults.

You think that's impossible? The Canadians and Irish don't - and they have proved it. Fundamental to a change back to thinner children is to solve one great problem. How do we get our children to eat fruit and vegetables, and to stop munching on crisps and chocolate bars, and tippling on fizzy sugary drinks?

The answer is in a brilliant new computer programme called Food Dudes. The principle relies on the fact that if children are given a small amount of a particular food every day they will begin to like it. Try to introduce, say, red pepper, to a class of children and to begin with not one will admit to liking it. Keep bribing them to eat a little every day for two weeks, and they will all love it.

Ah yes, you say, but how do you bribe them? That's where Food Dudes comes in. There are four of them: they are teenage superheroes.

They are in a constant battle against General Junk, who is intent upon stealing all the world's fruit and vegetables. Naturally the Dudes sustain their superpowers by eating the right stuff. Apparently it's very funny and hugely accepted by the children.

Sounds a bit fatuous? Don't tell the Irish that. The Food Dudes programme was used in 150 Irish primary schools. It was meant to continue for more than five years. It was stopped after two because it was so successful in changing the children's eating habits.

All Irish children between four and 11 are now taking part with the blessing of the government. In the first year of the programme, the children's average daily intake of fruit rose from 49 to 93 grams a year.

Best of all were the results in children (one in five of the total) who ate the least fruit and vegetables at the start. They raised their daily intake from one to 52 grams in the same time.

Just getting the children to watch the programme, and giving them stickers for eating more fruit and vegetables, was enough to produce this huge improvement. As is often the case we in the United Kingdom are lagging behind.

We are about to start pilot trials' of Food Dudes here. I wonder why we don't take the Irish and Canadian (the Canadians had a similar experience) at face value and get on with introducing the scheme countrywide?