I was regularly told that having two kids wasn’t twice as hard as having one – it was exponentially more difficult. I can’t say that I’ve found this to be true as of yet. Sure, it can be a little tough supporting the baby with one hand, holding the bottle in the second, and then fending off the over-eager attentions of a toddler with the third, but overall I’d put the addition of another member to our family at around 1.5 times more difficult than before – so it’s not all that bad.

Of course, that’s probably because Rosie is four weeks old, so she mostly only sleeps, feeds, poops and cries. When she’s just as mobile, inquisitive and determined as her 28-month-old sister, I imagine I’ll revise that figure upwards, but for now we’re certainly coping.

But that’s not to say it hasn’t been bloody difficult.

When Izzie came to the hospital to meet her little sister, she was so excited that the first thing she did was to slap the bed twice. And then, without missing a beat, she grabbed the nearest bottle of milk and tried to ram it down Rosie’s throat.

You see, to Izzie, Rosie is a doll – a flesh and blood doll she wants to cuddle and kiss and feed and change and do all the things to that a parent does. Which is all well and good, except I’ve seen how Izzie treats her dolls, and Rosie wouldn’t last thirty seconds without a dislocated shoulder or worse. It’s a sobering thought that the greatest threat to my second-born is not the dog, not the cat – it’s my first-born.

It has been difficult convincing the wider family of this basic reality.

‘Well I trust Izzie,’ said one with great pomposity in response to this statement, as though trusting a toddler with a baby is a sign of virtue instead of gross negligence.

‘I think she’s lovely,’ I replied, ‘but you never know what a toddler might do.’

‘Only a child with mental health difficulties would harm a baby,’ this person went on to say, clearly believing toddlers are in complete control of their emotions, have mastered fine motor skills and hand-eye coordination, and fully understand cause and effect.

There’s no cure for stupid.

So the past month has involved extremely careful supervision alongside the usual aspects of baby care. We’ve had to keep a certain distance between the two girls until Izzie can understand how to be gentle, which has caused plenty of tears and tantrums. Izzie wants to hold Rosie, and rock her, and get in the pram with her, and stuff her dummy in her mouth, and open her eyes when Rosie isn’t awake, none of which we can allow. But we have taken steps to alleviate this tension.

I instituted a rule from the word go that when people come to the house they have to greet and make a fuss of Izzie before allowing her to introduce them to her little sister. Furthermore, we involve Izzie in all aspects of childcare by encouraging her to fetch the changing mat and nappies and wipes, and she sits with us during feeds, and we make sure we spend plenty of time hugging as a group.

It’s had the effect of avoiding any jealousy, giving Izzie some sense of ownership of the situation, and encouraging her to love her little sister.

And, without a doubt, love her she does.

When Rosie cries, Izzie tries to comfort her – well, on those occasions she doesn’t put her finger to her lips and shout, ‘Shush!’

She’s also rather conscientious about keeping Rosie involved, telling us to take Rosie with us, to give her a hat, to give her milk, to change her nappy – which is lovely.

And Rosie responds to Izzie in ways she doesn’t to us. Now that Izzie is finally cottoning on to the fact she’s not allowed to touch the baby, when Rosie lies on the floor or sits in the bouncy chair, Izzie often lies and sits in front of her and tells her stories and sings and giggles, and you can see that Rosie is being stimulated by it. They have a connection to each other, as siblings and as infants, that we don’t seem to have with them as adults.

I mean, there are some teething troubles – Izzie doesn’t want to go to bed because the baby’s still up; she wants to be carried because the baby’s carried; when I’m rocking the baby in my arms I find Izzie clinging to my legs; and whenever Rosie is out of the car seat, Izzie climbs into it and makes it her own – but these are all normal, I think. Other than the clumsy roughness, Izzie is the very model of a doting big sister.

Although tere has been a really weird development: Izzie has become incredibly squeamish about poo.

Every time the baby poops, Izzie says, ‘Me not touch it, daddy, me not touch it.’

‘You don’t have to touch it,’ I reply. ‘Nobody’s making you touch it.’

‘Not touch it, daddy.’

The most hilarious manifestation of this was the first time Izzie held Rosie on her lap. I surrounded her with cushions, including one across her thighs, sat close beside her, and gently placed Rosie down. Izzie looked like the cat that got the cream, the happiest I’ve ever seen her.

And then Rosie did a noisy poop.

I’ve never seen Izzie move so fast. ‘Not touch it!’ she screamed as she somehow slipped out from under the cushions and over the arm of the sofa and off in the blink of an eye.

We think it’s because she went to her mother’s baby shower shortly before Rosie was born where they played a game involving putting strange substances into tiny nappies – peanut butter, chocolate, Marmite – and getting people to sniff and taste it to correctly identify the substance.

And now Izzie is traumatised.

Thanks mummy.