How easy is it to forget your children?
David Cameron's daughter was accidentally left behind after a visit to the pub. It's a scenario that's familiar to many parents, writes Kathryn Westcott.
For people who don't have children - or for those parents who are super-organised - the idea that a child could be left behind by a parent is simply outrageous. Forgetting your keys or wallet is acceptable but never a child.
But there are many parents who will identify with that feeling of horror when the realisation dawns that a child has been left behind somewhere. The Camerons were said to have been "distraught" when they realised that eight-year-old Nancy had been forgotten when the family left for home in two separate cars.
It's a heart-stopping moment - one that my family experienced not that long ago. Anyone with children will know that trying to get a group of them out of the house - shoes, hats, toilet runs - often needs to be planned with military precision.
And if there is a large party of folk to be extracted from the house, one parent may set off with half the gaggle, leaving the remainder with the other.
In our case, we streamed off down the road for a family event at the local church, three generations in tow. It was only when one five-year-old asked where his similarly aged cousin was that panic set in. Frantic messages were verbally sent between the grown-ups, until we discovered that he hadn't been seen since we left the house. After a mad dash down the street, we discovered him at home, oblivious to the alarm that had been caused by that moment of parental negligence.
Like the Camerons, one parent simply assumed he was with the other.
Justine Roberts, of the Mumsnet website, says that this is a familiar scenario for many parents.
"Many people will have some understanding of how this happened to the prime minister and his wife. Particularly if you are a family with two cars, there is the assumption by one parent that the other parent has a particular child. Everyone can see how it happens - particularly the more children you have - when you become outnumbered."
She says that any inference that the Camerons are not good parents or that the prime minister is unfit to run the country is "cynical".
"It's a case of but for the grace of God go I," she says. "Kids are good at rushing off at the last minute - going off to the toilet without telling anyone - sneaking into the cars of other people in the group. I have four children and I've probably lost all of them at some time or another."
From the messages left on parenting forums and stories that have been shared with readers and listeners to the BBC, it seems many parents have forgotten a child.
Rod Symmons recalls the time his daughter, who was four at the time and a bridesmaid, was left behind after a wedding.
"The reception was held at the South of England Showground and we were the last to leave," he told the BBC.
"My wife and I were in separate cars and each thought Jenny was with the other. By the time that we discovered she wasn't, the building had been locked up.
"Desperate by then, we found someone to open it but could not find her inside. My wife then remembered that she had seen some of the older girls riding in the lift earlier in the day and went to look.
"Sure enough Jenny was inside the lift, but not tall enough to reach the buttons. She was just beginning to panic and I shall never forget the relief of finding her."
Leaving a child inside or outside a shop appears to be the most common misdemeanour.
Many parents excuse such behaviour by arguing that they are often simply functioning on autopilot, that they are tired and distracted. One mother said she left her week-old baby in the Post Office because she "wasn't used to having a baby".
Father Alasdair McFarlane told the BBC he accidentally left his six-month-old in a shop.
"I went to buy a newspaper leaving daughter in pram outside. I then proceeded to walk out of shop without collecting the pram. My wife was not happy when I returned home," he said.
There have been numerous studies indicating that people are becoming increasingly forgetful as a result of modern hectic lifestyles. Researchers have labelled the condition "busy lifestyle syndrome", with stress being the possible culprit behind day-to-day memory lapses.
"Parents are increasingly busy," says Roberts. "In many cases both are working long hours - these are easy mistakes to make. Of course, it's horrific when it does happen, but it's a function of all the rushing around that people are doing.
"If it hasn't happened to you, you're either obsessive or lucky."
Every now and again stories at the other end of the spectrum will hit the headlines.
In 2008, a child was left at an airport in Israel after her parents accidentally took a flight to Paris with four of their five children. Most parents writing on forums said there was simply no excuse for this level of negligence.
And there have been incidents of forgetfulness that have had tragic consequences - typically involving children left in cars on a hot day.
Leaving a child behind is a nightmare for any parent - but it is one that many parents have to admit has happened with them.