Tell today's children how things used to be in the backs of cars and watch the looks of disbelief dawn in their appalled eyes. Explain the carefree absence of moulded seats and boosters. Explain how there was no rear of a car so small that it couldn't be made to carry five children by the simple expedient of getting everyone to budge up and/or sit on the smallest person's head. Explain how you travelled for almost ten formative years in the back of an Austin 1800, and the closest thing that you ever saw to a belt was on your brother's shorts.

Young people don't begin to grasp any of this. They have been raised in an era of personal cup-holders, seat-back tray tables and hand-crafted crumple zones and borne through the streets in splendid isolation, like kings.

But they had better wake up, for the age of shrinkage is upon us. Experts say that soon nearly everybody will be living in a city. They don't say which city - and if you're lucky, it won't be yours.

But the broader point is, if we're going to drive around at all by then, it's going to have to be in something only slightly bigger than the bubble in an Aero bar.

Your children should know, then, that their days of being delivered to judo behind tinted glass in a piece of pre-cushioned, over-upholstered sub-military hardware are numbered.

The urban micro-car is coming, and your kids are going to have to learn to like driving with their feet in their ears, the way that you used to. Or worse, with their brothers' feet in their ears. And they are going to find out what real pins and needles feel like.

Bouncing along on the coming wave is the Toyota IQ - less than 3m long. Toyota recently got some IQs out for some journalists to play with.

And everyone stood around saying, “Great model for the car. Now, where's the car?” But that was the car - a cute blob with a tough, squat stance and, astonishingly, four seats, with proper belts and everything.

Here's how you get the IQ going. You pick it up and swipe it backwards across the carpet a few times, until there is a nice build-up of friction in the rear wheels. And then you set it down and watch it ping off towards the skirting board.

Oh, all right, then. Not really. You get in and turn a key, pausing only to note the surprisingly acceptable amount of room, not only for your shoulders and the shoulders of the person next to you, but for two further pairs of shoulders in the back.

So, by what miracles of compression and micro-technology have Toyota achieved this ground-breaking Doctor Who-style trick with the dimensions of interior space? Well, with a set of nips and tucks that are certainly clever, but which car manufacturers could almost certainly have arrived at years ago, if they hadn't been concentrating on shipping out family tractors.

They have slimmed the petrol tank down until it resembles a giant roasting tin, and placed it under the seats. They have built a much smaller than usual air-conditioning unit, but without, allegedly, sacrificing any of its power. They have made the seat-backs thinner to increase leg room, and the doors thinner to make room for shoulders. And they have done some especially cunning business with the steering column, enabling the wheels to sit just ahead of the steering wheel, and the car to end very shortly after that.

The first thing we were invited to do in the IQ was take it through a small slalom of cones that I wouldn't have backed myself to clear on a child's tricycle. It wriggled right through them, though, and carried on wriggling, out on the streets, where its quick, jinking nature encourages you entirely to rethink your approach to parking spaces.

“What about that slot over there?” you find yourself wondering. “In between those two dustbins. Or how about that one, underneath that other car?”

And incredibly, the IQ neither whirrs like a hairdryer, nor juggles your head against the ceiling every time you catch a bump. It is properly upholstered and suspended and its one-litre engine hums and clears its throat sensibly, like a full-sized hatchback. Which I suppose it ought to, given that it is priced like one.

But at least you get some safety for your money. Somehow there are nine airbags on board. Lord knows where they put them, but it must be like being inside a duvet when they all go up.

So it's fresh, it's frugal, and it's full of life-saving cushions. Even your kids could learn to love it. But there's the handy thing: even if they don't, you won't hear them complaining because they will be sitting with their knees in their mouths.

Top speed 93 mph

Average consumption 65.7 mpg

C02 emissions 99 g/km

Eco rating 9/10

At the wheel Ronnie Corbett

On the hi-fi The Chipmunks

In the glovebox KitKat Kubes

Bound for Legoland

Buy it because: you're big enough

Rating 8

Price from £9,494