Royal baby: The 'heir and the spare'
It is a common refrain among many parents that baby number two is not quite the centre of attention in the way baby number one was.
It does not mean they are any less loved but life does still tend to revolve around the older sibling.
It is hard to compete with their "firsts": walking, talking, going to school. By the time the second child achieves the milestone, the parents have already seen it all before.
If your average first-born child is a hard act to follow, imagine being the sibling of the heir to the throne.
There is no question about Prince George's destiny. One day he is expected to be the king.
In less healthy times, his younger sibling would have been considered essential should the worst happen - hence the phrase "the spare to the heir".
In the last century premature death was not the only reason behind the "spare" being drafted in.
The Queen's father enjoyed a relatively normal, private family life right up until the abdication of his older brother, Edward VIII in 1936. George VI, as he became, filled in for his older brother admirably, if somewhat reluctantly.
Few would argue that the most recent "spares" - Princess Margaret, Princess Anne and Prince Harry - have been dealt an unlucky hand, but it must be a curious position to hold.
The abiding image of Princess Margaret, the Queen's younger sister, is of a woman who was able to lead a much freer existence - holidaying with great and good in Mustique and enjoying the trappings of royalty unencumbered by responsibility.
However, she was at the centre of a media storm herself in the mid 1950s when her relationship with divorcee Peter Townsend became global news.
The relationship came to an end with a public statement: "Mindful of the Church's teachings that Christian marriage is indissoluble, and conscious of my duty to the Commonwealth, I have resolved to put these considerations before others."
Her biographer Christopher Warwick argues that despite her image as a "good time girl" she was in fact "totally dedicated" to her charity work and "totally dedicated to her sister as the Queen". Not so carefree after all.
Princess Anne only occupied the position of "spare" until the birth of her younger brother Prince Andrew when she was aged nine. He then leapfrogged her in the line of succession.
Perhaps it is due to her position as the second born that Princess Anne seems to have managed to combine her royal duties with a family and working life with some success.
She had her own career as a sportswoman, winning both the European Eventing Championships and a place on the British Olympic team in 1976.
She has raised two children who have no royal status and have their own careers and families.
The Princess Royal's private life has involved divorce and remarriage but throughout, the media spotlight has usually been trained on her older brother.
As someone who clearly dislikes being in the limelight, one would imagine Princess Anne is rather pleased to have been the younger sibling.
'Find own role'
And so to Prince Harry, the most recent "spare".
As one of the so-called "Magnificent Seven" with the other royal A-listers (the Queen, Prince Philip, Prince Charles, Camilla, William and Kate), he is expected to be a high-profile, hard-working member of the family.
But he has also been given the freedom to serve on the frontline in Afghanistan. Security worries would have made such active service impossible for his older brother.
Prince Harry's indiscretions, which have been well reported, have done little to dent public opinion of him.
Would people have been quite so forgiving if William had been photographed cavorting naked in a Las Vegas hotel room?
That said, Prince Harry is perfectly placed to offer advice to his new niece or nephew who will be fourth in line to the throne, but never expected to be monarch.
Mr Warwick says their position will always be a "secondary one - and rather like Prince Harry, he or she will have to find their own role".
He adds: "They'll have to find their own charities, their own causes, and who knows, maybe they'll decide to take a completely different path in life altogether."
No doubt Prince Harry's wisdom to the new "spare" will be shared behind closed doors. But it may include an instruction to uphold Royal Family values, although if you do misbehave… the telling off won't be anywhere near as bad as if Prince George had done it.
In that sense, the Royal Family dynamic is not so different from ordinary families after all.