Yes I know any primary-school age child could point out my faulty maths, but it's true. Two is double the work of one, three doubles it again. There's something about odd numbers that is makes it all so unwieldy. We have two hands; there are only, at most, two parents; the special offers on the back of cereal packets for cheap entry to Legoland are only for two children.
2. YOU'LL NEED TO BUY A BIGGER ONE OF EVERYTHING
That Prius you smugly drive around will have to go. Who are you kidding with your eco-friendliness anyway, you've just done the most environmentally aggressive thing by over breeding. And then you think, if we're going to get a bigger car, we might as well get one that seats seven and before you know it you're driving a van and giving every child in the neighbourhood a lift to football matches and birthday parties.
3. THE CAR'S EXPENSIVE, BUT IT'S NOTHING IN COMPARISON TO A HOUSE
Two-bedroomed places are bad enough, three is another category again but there's no jump higher than going to four bedrooms should you wish each of them to have their own room. Far easier to let those sharing bicker with the age-old device of a belt strung across to create an iron curtain between them.
4. AND YOU'LL END UP LIVING IN A&E ANYWAY
The combination of an extra child and a reduced ability to keep an eye on them is lethal. Our eldest has been so many times that they now whisk him into a separate room to ask him if he has a social worker. Our youngest pulled a fashionable but very heavy stool onto her face and they had to call the maxillofacial surgeon. The middle one, in a desperate bid for attention managed to wedge a pencil lead so far down her inner ear that it needed two doctors and three tools to pull it out.
5. WITH THREE, THEY'RE 50 PER CENT MORE LIKELY TO DO EVERYTHING
This includes be off school just when you can't take a day off work. Fifty per cent more likely to come down with chicken pox just before you go on holiday. Fifty per cent more likely to vomit on their bed sheets. You get the picture.
6. YOUR FAMILY AND ONE OF YOUR CHILDREN ARE STUCK IN THE MIDDLE, AN INBETWEENER
The really posh (or feckless or both) have four kids or more to show how fecund and rich they are. The sensible have two. You with your three are neither a big family nor a neat one, you're just a big 'meh'. Apparently two to three is the most stressful transition because once people get to four, they stop caring. Similarly, one of the children is always in the middle. They have to sit in the uncoveted seat without a window in the car, but also in life more generally.
7. EVERYONE MAKES ASSUMPTIONS AS TO WHY
If you've got two of the same sex, they'll assume you're trying for whatever you're missing as if children were stickers in a Panini album. If, god forbid, you fail to produce the boy/girl of everyone else's dreams, you'll be faced with much head-tilting sympathy despite holding your lovely and loved child.
8. THERE WILL BE INCREASED LEVELS OF PARENTAL INVOLVEMENT IN MODERN LIFE
Just because your own parents seemed to cope easily, doesn't mean that you will. Remember parent was only a noun back in the 70's and 80's, rather than the hard-working verb of today. I don't remember my parents getting much involved in my education or life - so long as we were fed and watered they were doing their job.
But now, every day brings children laden with A4 sheets from school requiring signatures, tear-offs, money, costume creation, parent helpers. It doesn't get any easier either. When I was young, nobody would dream of their parents coming along with them to university open days. Now, universities put on special Q&As for mum and dad with nice biscuits and everything.
9. YOU WILL, AT SOME POINT, SAY HOW IT'S ALL WORTH IT AND YOU WOULDN'T WANT IT ANY OTHER WAY
And it's true, I love the myriad different relationships my children can have with each other and the way they form a cute little gang against us. Besides, as someone much wiser than me once pointed out, the best reason to have a third is so you can stop endlessly debating about whether to have a third or not. Take note, Duchess of Cambridge.