It's all about the kids now.
That realisation takes a little while to sink in. For the first couple of hours I can pretend that everything is the same as it ever was, that we're a bunch of friends hanging out and drinking cocktails and having carefree fun, but it's about 10pm that that myth is dispelled forever.
Like Cinderella fearing a coach rendered as a vegetable, my friends start getting these worried looks. They start checking their watches, conferring with their partners, nodding their heads and downing their drinks.
They look a little sheepish as they make their excuses: "Well, the babysitter has to get home. We only booked her until 10. And we've gotta be up really early in the morning, you know?"
Kids: they're small, but they take up a gigantic amount of space. I don't have any of my own, but I've recently started travelling with close friends of mine who do, and the difference is shocking.
We're in Fiji for a wedding. This, traditionally, would be a time for revelling, for doing "the worm" on a makeshift dance floor at 4 o'clock in the morning.
This friend group of mine used to go on annual holidays together, when we'd hire a houseboat for a long weekend and spend it either partying or recovering from the partying and getting ready for more partying.
But things have changed. Matt and Kylie have a six-month-old. Shelly and Aaron have a three-year-old and a one-year-old. Emma and Chee have ... I don't know, something similar. It's hard to keep track after a while. At least I know their names.
This wedding is a destination job, the venue, the Intercontinental Fiji, chosen not just because of its luxurious abodes and beachside locale, but because childcare is cheap and reliable. You have to think about these things, I'm told. It's all about the kids now.
By the time I arrive on the first night, the little tackers are nowhere to be seen. They're safely in the care of fairly large and extremely friendly Fijian people. Those who sired them are free to drink and celebrate - until 10pm, that is. Then they make their excuses and it's the childless few left to prop up the bar.
Mid-morning the next day I wander bleary-eyed down to the pool and there my friends are, tossing their kids in the air, or yelling at them to be careful, or photographing them, or doting over them, or sloshing sunscreen on them. They flash smiles and then get back to the task at hand: the kids.
The parents have all been up for hours, talking to each other, probably, about their kids. Comparing notes. You know when people first break into the property market and all they can talk about is their house? Same happens with the kids, only times about a thousand.
There's progress to discuss. Should they be doing this by that age? Should they have started doing that? Should they really be putting that in their mouths?
In a few years' time there'll be school grades to compare and sporting prowess to boast about but for now it's just whose kid does the stinkiest poo and who has the most allergies.
As a non-parent, you're tactfully left out of these discussions, free to wander over to the adults-only pool and bask in its child-free tranquillity, which would be great if any of my friends were there to share it with me.
Meals have changed on this trip. We eat early these days. We pull up seats and the first topic of discussion is what the kids are going to eat. Is it healthy? Will they actually eat it?
High chairs are organised, bibs are adjusted, food is slopped everywhere, an eye is kept on walking kids, immobile kids are wiped clean. There's screaming and the odd tantrum - sometimes even from the children.
I don't mean to complain here. My friends are wonderfully intelligent, caring people - there should be as many of their progeny in the world as possible. But wow, travel among this group will never be the same again.
We're no longer thinking about ourselves all the time, but about the little people storming around the table slapping me on the back to see if my sunburn still hurts. We're planning child-friendly activities the whole family can enjoy. We're posing for a million photos in the hope that in one of them - just one of them - every child will be looking at the camera.
We're spending nights out silently dreading the screeching on the morning after. We're comparing notes about babysitters. We're calling it quits at 10pm.
Because it's all about the kids now.
Did travel change for you once you had kids? Are you a childless person who has travelled with a family? What was your experience like? Post your comments below.