Nobody can see inside another family's life, not really. But the fact is that when a politician suffers difficulties or tragedies involving a child - we think about that lawmaker a little differently, much as we think of men who have been to war.

Without wishing hard experiences on any parent, it is natural that we should feel a kind of reassurance when those whose job it is to weave social safety nets are, at least, aware of what it feels like to be helpless in the face of unkind fate.

David Cameron himself has said - although with emphatic modesty denying the title of “carer” - that helping to look after his severely disabled son Ivan at the start of each day “sharpened my focus on the world of care assessments, eligibility criteria, disability living allowance, respite breaks, OTs, Sencos, and other sets of initials”. He has in his years of public prominence neither exploited nor hidden Ivan; in this his behaviour echoes that of Gordon and Sarah Brown who displayed equal openness and dignity when they lost their first child Jennifer, and who allowed to be made public quietly their youngest son's cystic fibrosis.

These things command respect, whatever your politics (particularly, perhaps, where fathers are concerned. It is hard to remember much sympathy of any kind for Sarah Palin. Indeed, her young child's Down's syndrome made critics readier to attack her for getting back to work so soon). Like it or not, we all pay more attention to a problem when it afflicts one of the shining ones: the famous, the important, the handsome young potential prime minister with the privileged upbringing and the beautiful wife.

So the death of Ivan Cameron at six-years-old is something that makes us pause and think about that family, and about all the others who look after children with serious disabilities and limited lives.

Ivan and the family did well: babies with this rare Ohtahara syndrome very often die before their second birthday. He has been fought for hour by hour since he was born; his relative longevity can only make the grief all the sharper. His father described him as wonderful but has been frank about the initial horror of discovering that his first child was so grievously hurt by Nature: “The news hits you like a freight train. You are depressed for a while because you are grieving for the difference between your hopes and the reality. But then you get over that.”

It is that public acknowledgement that has been valuable, whether or not Mr Cameron becomes our national leader. Voters, he said at the time of his domestic filming, “have a right to know a bit more about you, your life and your family, what makes you tick and what informs your thinking”.

He is right. And that gap between hopes and reality, between illusory glamour and the inescapable toughness of life, is one of the things that politicians and public figures can most usefully demonstrate. It is a fine line to tread, and family privacy is precious: but there is real benefit when they are prepared, without exploitation or mawkish self-pity, to share the shocks and griefs of life.

The parents of disabled children in particular have an invaluable lesson to teach. For all our lip service to equality and political correctness, we tend to exist in a callously competitive culture. The loathsome term “value-added” is routinely used in education, even of infants, as if the basic child were never quite valuable enough. Among adults “loser” is an insult, not a term of sympathy. Parental pushiness and boasting are commonplace, more common, it sometimes seems, than genuine appreciative affection.

Years ago, writing about mothers competing over their small children's prowess and progress, I said that we could all learn a thing or two from the parents of children with mental disabilities, since those parents accept early on that the only marker of success or failure is not comparison with the kid next door or some imaginary set of targets, but with a child's own progress in overcoming difficulties. They are forced to be grounded. My publisher at the time demurred, saying that this was a “depressing” thought. I felt that it was a profoundly encouraging one.

The Camerons' loss is immense, and should not be belittled. It is not, as some old wives may chunter, “a mercy” when a young member of any family dies, however much is wrong with him or her. The child, however disabled, has had a place and a value and a role among siblings. He is a presence in the family: he affects its shape, its arrangements, its jokes. His small triumphs of communication and enjoyment are part of the family's communal wealth. Brothers and sisters learn much, however hard it is and however it affects their pleasures at times.

In her remarkable 1988 book The Other Child, Linda Scotson describes the contribution that her daughter's childish determination and refusal to accept that he could not be a playmate, made to the rehabilitation of her seriously handicapped son Doran.

In the story of Christy Brown, the Irish author with severe cerebral palsy who wrote My Left Foot, his development was enhanced by being regularly dragged round Dublin by his brothers on an old go-kart as they saw no reason to leave him out.

All but the most dysfunctional families show a remarkable ability to go with what they've got, give it their best shot and patch up shortcomings with love, ingenuity and acceptance.

The loss of Ivan will have left a gaping hole in the Cameron family. But the rest of us can get some benefit from contemplating, from a decent distance, the way he lived and died.

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