IT is the classic start to chilling drama. A collection of people, all of similar age and temperament, is gathered in a room. Something is due to happen. Will it be an inspector calling, bad news in his notebook? A nice surprise, or otherwise? By the pricking of my thumbs, something unfamiliar this way comes. Open, locks, whoever knocks … “I can hear them coming,” says someone as a wave of noise crashes down the corridor. “Stand by your beds,” says another.

Who are these terrifying creatures approaching?

Happily, it is just a gaggle of your average four-year-olds, come to visit elderly people in a care community, as seen in a two-part Channel 4 documentary, Old People’s Home for Four-Year-Olds. If you watched it on Tuesday and last night then you will know what a treat lay ahead. If you missed it, head for the All 4 catch-up service pronto.

Channel 4 has often pushed the boundaries in the past, but this was truly radical television for the age, showing as it did, wait for it, young and old mixing. Not just mixing but actively enjoying each other’s company. What madness is this, you may be wondering.

The idea for the programme came from a successful experiment that took place in Seattle 25 years ago and has since been repeated hundreds of times across America. The Bristol scheme, according to the programme makers, was the first of its kind in the UK and the first to assess medically what impact, if any, spending time with children had on elderly people’s mood, memory, and mobility.

It will hardly come as a spoiler to any grandparent that the results were overwhelmingly positive. Depressions lifted, creaky limbs moved more easily, optimism about the future returned. For those residents who took part, God’s waiting room, as one resident called the (very nice) assisted living community, became a joint that jumped. Judging by the amount of laughing, chatting, and wall-to-wall daftness going on the children enjoyed themselves too.

What was perhaps most surprising about any of this is that anyone should be surprised. But then we have become accustomed to regarding age groups mixing (intergenerationality to give the process its Sunday-best sociological name) in certain ways. We assume it happens naturally. Perhaps we regard it as a thing best avoided.

Overall, the prevailing story about the old and young in our society is a negative one, with both sides, when they get to a certain age, appearing to be at odds over everything from Brexit and pensions to housing and access to healthcare.

None of this is new. Young and old have looked at each other in incomprehension since Adam was a teenager. The only difference in Western society today is that the older generation have the money and opportunity to do something about it. They can, if they choose, avoid the young wherever possible. They can buy properties in age-restricted communities and gated ones. They can take holidays while the schools are in, cruise the world in winter. Advertisers and politicians court older people, businesses spring up to meet their needs. The health service gears itself to making them live longer, fitter lives. Sure, the old bodies and minds are maybe not what they used to be and, to quote one Billy Connolly, aged 74, old age is not for sissies, but for many this could be as good as it gets for older generations.

Contrast this with the lot of those just starting out in their adult lives. Assuming they receive a halfway decent education (no longer a given) and make it to university, they are at the beginning of a long road paved with debt. Finding a secure, well-paid job and bringing up a family will be harder for them than it was for their parents. Ditto getting on the housing ladder. As for pensions, stand back and wait for the hollow, bitter laugh that word provokes in the young. It is no longer men and women who are Mars and Venus, it is young and old. But what is to be done about it?

For a start, let us not become too misty-eyed about the past and the way things used to be. One of the many pleasures to be had from a visit to the People’s Palace in Glasgow is showing youngsters the “single end” exhibit. They peer into this recreation of tenement life as if it is the entrance to the ghost train. When told that this is not the bedroom of an only child from ancient times but the living, sleeping and eating space of an entire family not so long ago, the youngsters look as though they have just stepped off said ghost train after a particularly hairy ride. Ma, da, weans, often granny and grandpa too, all hugger-mugger in a tiny space. The horror, the horror. (I don’t know how much joy youngsters derive from the single end experience, but it certainly makes adults chortle, even if most of the parents who go there today are the X-Box generation rather than the shared toilet on the landing lot.) Let us have no nonsense, then, about how things were better when the generations lived together. Only the very rich and the very poor ever lived in one house, and only the big hoose dwellers, with enough room still for servants below stairs, got a good deal out of the arrangement.

Let us not go overboard, either, over the results of the Bristol experiment, cheering as they were. This was a small-scale project, the adults who took part had volunteered, and the get-togethers were relatively brief. There were tears and a plea to go home at one point (from a youngster, not an oldie).

It is worth noting, too, that the high cost of childcare means some grandparents already spend a lot of time with their children’s children. Having retired from one job they find themselves with another, one that they adore but which leaves them exhausted as well.

Yet what the Bristol project showed, what our own experience tells us, is that young and old can benefit from spending a bit more time in each other’s company. We live, we learn, we see things with different eyes, we realise things are not as bad, or as good, as we assume. The alternative, a wider gulf than there is now, benefits no one.