And then there were three - What's in store for Kate and William?
Just what impact will a third child have on the Duke and Duchess of Cambridge? While the royal couple will have plenty of help to hand, the new arrival will inevitably change the family dynamic as our three writers - each with three children - explain.
Alex Kane: ‘New arrival has seen daughters rise to challenge'
William and Kate inhabit a very different world from my own, yet I'm pretty sure that they'll soon discover that when it comes to children-even heirs to a throne-three isn't a crowd. With two the dynamics is so predictable it's almost like it's set in stone. They either gang up against you or try and force you to take sides; which leads to all sorts of stand-offs, melt-downs, tantrums, groundings, door-slamming and monumental huffing-and that's just from me!
In our particular case the age gap between Megan (18) and Lilah-Liberty (7) brought its own dynamics, particularly when it came to deciding what films to see, where to go on a day out and what, precisely, constituted family viewing on television. Both objected to my entirely arbitrary banning of the X Factor, Big Brother and I'm A Celebrity, although, as I finally discovered, got round it by retreating to Meg's bedroom (supposedly to watch a 'nice, wholesome Disney movie' on Meg's television) and watching the programmes on her mobile phone.
The other problem with two children - even two with an 11-year difference - is that they rarely ever want to do the same thing at the same time. Mention that you want to go to mini golf and one will say yes, while the other wants to go to W5 or ice-skating, or just about anything else. By the time we've argued back and forward for an hour or so (by which time I just want to go to my study and read Sherlock Holmes) and reached a compromise which nobody really wants - like a walk in a park or a beach - we've all become terribly grumpy.
It's actually fascinating to watch the girls during those moments. They're both learning valuable lessons about staking out their own territory and standing up for themselves; and they're also ruthless in both their willingness and their ability to play off Kerri against me by calculating which of us is more likely to do what they want to do (I hate anything involving sport, bicycles or swimming). Anyway, for some reason I've never quite understood, Kerri is always on the winning side. Ironically, she's always the one who talks most about compromise - a compromise which is always her first choice, as it happens.
The arrival of Indy - and thanks to the hundreds of you who found a way to make contact after my Letter to Indy was published in the Belfast Telegraph - has already changed the dynamics in the house. Both girls have risen wonderfully to the challenge (as well as the noise, smell and early rising) of their new brother. And the very fact that it's a boy has, I think, made a difference. They don't see him as a doll to be fought over and dressed up; instead, they see him as a brother to be loved, protected and welcomed. It has made both of them grow up - albeit in slightly different ways.
It has also changed the dynamics between us and them, because we need to spend so much time with Indy. That has pushed them closer together and even the tone and nature of their conversations has changed in the past seven weeks. Both of them, for the first time, have also recognised the challenges facing parents with a baby and, knowing that we are limited in what we can do at the moment, have become less demanding in terms of what they want from us.
Every child is a blessing.
But three seems - so far - to be the perfect number.
Karen Ireland: 'Teo was the biggest shock of my life but he was also my miracle'
I never thought I'd have much in common with Kate Middleton (below), but now she is in exactly the same situation as I was 13 years ago.
As a mum of two young children I found out unexpectedly that I was pregnant again. When I say it was unexpected I was told I couldn't have any more children and was scheduled for a pre-hysterectomy op the morning before I found out I was pregnant.
I just had a feeling in my body that something had changed and I will always thank God that I had the sense to check it out and did a pregnancy test before the surgery.
No one was more shocked than my consultant who was treating me. I had always imagined I would have two children and when I was told I couldn't have any more that sort of settled things for me.
I was worried sick about managing three as when you have two there was one each to manage but who would attend to the third?
Then there was the matter of the sex. I had two young boys - Jesse, who was then four, and Korey was just two.
Everyone told me it was a girl, and I make no excuses for the fact that I longed for the third baby to be a girl as my mum had passed away and I wanted to have that mother-daughter bond.
Even the consultant said it was a girl at the time and we were over the moon. There was even a small pink babygro from DisneyLand in Paris which was purchased.
However, when Teo was born he was rushed to special care so all thoughts of whether it was a boy or girl went out the window and all that mattered was that my tiny baby was healthy.
Two weeks later, he was allowed out of special care and I bought my third child home to the caravan which I was living in at the time as my house was being built.
Dealing with three young children wasn't easy and I do think Kate and William will be in for a big shock.
With three children, there is always someone who wants something. Sleep becomes a thing of the past again as a new baby upsets everyone's routine and wakens the whole house when crying - and then you have three to get back to sleep with someone always ending up in bed with you.
Teo was the biggest shock of my life but he was also my miracle. He completed our family.
Life has never been the same again as he is the livewire of the household and always making or creating something.
Life is never boring as a mum of three and I must admit I never think now about what it would be like to have a girl as I have a close bond with each of my children.
The royals will be fortunate as they will have lots of help and support when their new baby comes along - and they will need it as with three you really do need eyes in the back of your head.
As for me, though? I wouldn't have it any other way.
Alison Fleming: 'They'll not have to fight over who gets an extra 10 minutes of sleep'
My first thought on hearing that the Cambridges were expecting a third child was that they would be having a very different experience to most parents blessed with a brood of three.
Nannies, massive houses and not having a nine to five existence will mean they'll be spared most of the chaos that goes with a third baby.
That said, I wouldn't swap my life for theirs, as we didn't have to do it in the glare of the public eye as they will.
While I have no doubt that they'll get stuck into the bread and butter of child rearing with baths, spoon-feeds, nappies, etc, it's hard to imagine them having to fight over who gets an extra 10 minutes of sleep.
Perhaps they will want to experience the sheer hard work that goes with extending your brood beyond the 2.5 average, but why would you if you didn't have to?
That 2am cry is like a shard of ice going into your heart. I will admit there were some nights I would easily have sold my soul for a straight eight hours of sleep. That was for all three of them.
On learning I was pregnant with my youngest daughter Kitty, my initial elation quickly turned to mild panic as I wondered how we would manage. You only have two hands, and even with two parents, you're still outnumbered.
Having just come out of the fog that comes with having two children 14 months apart, we were getting into our groove again when we learnt our family was expanding. Shoes could be put on without help, broken nights were no longer an issue and communication skills fully developed.
Going back to the baby years wasn't easy, but the joy of having another child quickly offset the military levels of organisation that were required for our busy house.
Unlike when Annie (13) and Finn (12) were babies, I now had two very willing volunteers (then aged four and five) who were delighted to be involved in the most basic of tasks. Everything from getting nappies to keeping their little sister entertained was outsourced to my miniature army.
The majority of the work still fell to my husband Damian and me, but someone once said (probably me) that if you have two, you might as well have 22. We just put our heads down and got on with it, ably assisted by grannies, grandas and aunties.
And despite the early morning starts, I grew to love the times when it was just me and her against the world at 5am, owning the day, knowing that those moments were all too precious and fleeting.
Going back to work after six months was tough, as I knew that I'd never again have the maternity leave that I'd cherished with Kitty. That said, it was a treat to have a cup of tea without fear of it getting knocked over, or even going cold as I dealt with the never-ending round of chores that a new baby brings.
I must admit that even though she's about to turn eight, she's still very much our baby. That will never change. I'm sure it will be the same with William and Kate and their new addition.