Kate Middleton's pregnancy: The perfect end to a jubilee year

Until late Monday afternoon, 2013 looked like being a pretty quiet news year in terms of festivals and celebrations. The Benjamin Britten centenary and another Ashes series were the best of some pretty thin highlights.

Well, fingers crossed, a bigger news event will now dominate the headlines. Without for a moment suggesting that the Cambridges actually timed the conception, the Royal family really has got this PR lark taped. If 2012 was Queen Elizabeth's year - whether she was apparently jumping out of a plane at the Olympics, or celebrating 60 years on the throne - 2013 now looks set to belong to her great-grandchild.

In and of itself, that is a pretty rare milestone. The last sovereign to meet a great-grandchild in direct line to the throne was Queen Victoria; that great-grandchild was Edward VIII, born third in line in 1894. Our Queen's great-grandchild will also be third in line, although she won't necessarily become monarch if she is a she.

A proposed constitutional change - that the eldest child of the monarch should become monarch, irrespective of gender - hasn't yet become law. But it is all but certain: last year, David Cameron announced that the 15 other Commonwealth countries where the Queen is head of state had agreed to give female members of the Royal family the same rights of succession as their brothers.

It's worth remembering, too, that, like the best horse races, the favourite to succeed to the throne doesn't always win; and outsiders often romp home. Nobody thought Princess Elizabeth, daughter of the then Duke and Duchess of York, had much chance of becoming queen when she was born in 1926. Everyone thought that, in the normal course of events, the Duke of York's older brother and heir to the throne, the Prince of Wales, would provide his own heirs. We all know what happened next.

Still, in the normal course of events, next year will see the arrival of the next monarch but two. The baby will be unlikely to succeed for half a century or more: while Edward VIII was 41 on his succession, George VI 40, and the Queen a mere 25, Prince Charles is already 64, and his mother looks in good shape for years to come.

Apart from the small matter of reigning over the United Kingdom and the Commonwealth, the royal baby will be like no previous heir in one big regard - the relative normality of his or her childhood.

How different it all was for the Queen. For her birth in her parents' Mayfair house, the home secretary, Sir William Joynson-Hicks, was present in the next room. The practice of having a government minister present continued until 1936 - for the birth of a minor royal, Princess Alexandra. Soon after, George VI declared that a minister was needed only for those in the direct line of succession; by the time Prince Charles was born in 1948, the practice had been abandoned as "neither a statutory requirement nor a constitutional necessity".

Charles still suffered from the peculiarities of an old-fashioned royal childhood. He and his siblings were left for months at home with nannies as their parents went on foreign tours. As for Prince William, he may have been the first future British king to be born in a hospital - delivered at the private Lindo Wing of St Mary's Hospital in Paddington, London, in 1982 - but, still, even in his youth, there remained a distance and formality to royal childhoods.

As the marriage of Prince Charles and Diana, Princess of Wales, hit the buffers, it was nannies who were responsible for much of the care of William and Harry. Both princes naturally formed strong bonds with those nannies, Tiggy Legge-Bourke and Olga Powell. In October, William cancelled four high-profile engagements in the North East to be at Mrs Powell's funeral in Essex.

Royal childhoods have changed, though, over the past 30 years. As have the childhoods of the classic, professional Sloane - the type who, in so many ways, the Cambridges resemble. At 30 - or 31, as Kate will be when the baby is born - the couple are still slightly at the younger end of the Sloane child-bearing spectrum. But, in other regards, they are just like their contemporaries: both university-educated, well-balanced, on kissing-hello terms with their surviving parents; both have sown a few, but not many, wild oats. In all likelihood, both will be nappy-changers. The omens are as good as they can possibly be for a secure childhood for the new arrival - not least with one set of grandparents who remain happily married.

It's striking, too, that the Duchess of Cambridge is older than most mothers of heirs to the throne, not least her late mother-in-law - the Princess was only 20 when she gave birth to Prince William. Prince Charles was 13 years older than his wife; of all the forces that destroyed their marriage, age difference has remained relatively unremarked.

On her wedding day and in early motherhood, the Princess was really still an uneducated, unworldly girl, scarred by an unhappy, lonely childhood and her parents' divorce; the innocent virgin foisted on a reluctant heir, who was still in love with his old girlfriend but obliged to carry out his one essential task - to produce a legitimate heir and a spare.

The Duchess of Cambridge had the same essential duty, but there is none of that other miserable emotional baggage filling her new home, Kensington Palace - once, too, the home of her parents-in-law. In fact, looking at her recent royal engagements, it's striking how very attached she is to her childhood. First she visited her old university, St Andrews, where she met Prince William, and then, only last week, she went back to her prep school, also called St Andrew's, in Pangbourne, Berkshire.

Incidentally, her pregnancy presumably explains why she took to the prep school hockey field in an inappropriate Alexander McQueen dress and high heels. She must have decided against any pre-planned game on medical grounds but, once she was handed a jolly hockey stick, the old urge must have struck her. Play up, and play the game, and all that…

How the republicans must be seething. Not only is another year of rose-tinted royal coverage guaranteed, but a whole childhood's worth - the first pictures of the baby, the christening, the first steps, the first public words, the first day at school.

Unfavourable media coverage eats away at the monarchy's support - as it did in the bad old anni horribiles of the 1990s. But several years of adoring baby pictures are manna from PR heaven. We may well marvel at the Rolling Stones being at the front of our consciousness for half a century, but we weren't inundated with cute pictures of Mick Jagger's baby lips from the day he was born in 1943. The Queen has been on the front pages since 1926.

Royal babies are different - we know and recognise them almost from day one. Only the most obsessive royalist looks on them with the same love as they do their own children; but only the most committed republican can resist building up some sort of attachment.

That is how the monarchy has survived for a thousand-odd years. The next 80 or so years of a royal Britain are suddenly looking even more secure.

Harry Mount is the author of 'How England Made the English' (Viking)