Jools at least had the good sense to leave a bit of time between each birth, but I do wonder if she knows exactly what she's letting herself in for. For as I've discovered, life is cute with one, manageable with three, but at times completely impossible with five. When you're officially "outnumbered", as soon as you've put out one fire, you're on to the next.
The fifth is the point at which mum and dad can no longer sit beside all of their children on the sofa; you can't hold all of their hands when walking along. With five, someone is always left out - and it can feel excruciating.
When Robbie popped out "like a bullet" (to quote the midwife) at 38 weeks, at first, inevitably, it was the nights that were almost unbearable. Instead of a night-time cuddle, more often than not, Ray and I began to kick one another in bed whenever Robbie - or one of his siblings - cried. "Your turn," we'd mumble, trying to clutch on to sleep. "I did the last one."
Even today, our arguments are all about time, taking turns or who is the most tired.
But what's really knocked me for six has been the fact that, despite having a child hanging from every limb, I sometimes feel surprisingly lonely.
Yes, my children, Lily, twins Tim and Joe, Evie and baby Robbie, all love me unequivocally. They bring me flowers, constantly want a cuddle or a "cawwy", and make me cry with laughter. But their needs - necessarily - eclipse mine. And they need a lot. Constantly.
While all children love their mums, by default, every mum is a sounding board, something for kids to take their frustrations out on, and someone on whom to wipe tears, wet fingers or worse. The feeding, brushing, entertaining and wiping means that you are always the last one on the list.
Recently, I had to go hospital to have a small lump removed from my leg. I drove myself there, sat alone in my hospital gown, was wheeled in, chopped up and dispatched, after which I had to drive home using my gammy leg for the accelerator.
And when I called my husband post-op, after a brief "how are you?", he broke into an anecdote about the difficulties he'd had getting everyone ready in time for school, which trumped anything I'd been through.
The final insult? Realising I was humming the Spongebob Squarepants tune in the car on the way home.
The positives of a large family
Clinical psychologist Linda Blair reassures me that there are many advantages to having a large family.
"It can be a happy situation - totally chaotic, but happy," she says. "Kids with lots of siblings tend to grow up with better social skills - they're learning the key skill of compromise.
"On the other hand, because there's less adult time per child; they may not have as much success as in school. Language is the key to academic success and the amount of linguistic input a child has between the ages of one and four is absolutely critical."
She says the ages of your other children are important: if the eldest are 12 or over, they will naturally help out with raising the new baby. "You'll be freer than you think. You can get a lot done, if you're careful with your praise of your older children."
She admits, though, that she has heard many mothers say an even number of children is easier, so the two parents can manage two at a time. "Also, children make friends in pairs, but in threes will often fight."
Having lots of siblings does seem to be helping my children to develop socially. As well as calling each other "babies" (apparently the worst possible insult), they've also begun to form cute friendships with one another, asking "are you alwight?" when someone falls down, and making tents under the table.
My eldest, Lily, six, is developing an incredible ability to manage her younger siblings. Comments such as, "Yes, you are a better runner than me," or, "Wow, I thought that was a real shooting star for a minute!" when being shown a blob of paint on canvas, demonstrate that she has learnt how to make others happy.
"I never wanted five"
I'm not a typical multiple mum. Despite being one of four myself, I'd always planned on just two children. And I do, sometimes, feel judged when I'm out with all of them, trying to keep an eye on everyone at the swimming pool, or strap them - wailing - into the car afterwards. But having stared infertility in the face, I am always aware of how lucky I am.
Blair says any couple planning to have a fifth child must agree that it's going to be a partnership. "The problems come if you feel you're doing it on your own."
I'm lucky to have my husband who, having taken early retirement, is able to be a truly hands-on dad. Jamie, similarly, seems to be very involved in his children's lives.
So although I'd warn anyone seeing the pictures of the Olivers' new arrival that life can be lonely with five, I've also got to admit that while I may never get to finish a hot cup of tea again, I'd thoroughly encourage anyone who's feeling a bit broody to join the "just one more" club.
After all, I may have constant exhaustion, a laughable pelvic floor and a pouch of twin-skin that no amount of sit-ups will shift, but I've also got a wonderful family whose happy laughter makes up for every gripe.
