Here's a long list, along with a list of carseats that have been tested "3 across" in those cars. A minivan or SUV would undoubtedly be easier to load kids in and out of, of course.

https://www.thecarcrashdetective.com/3-across-car-seat-guide...

There are plenty in the UK: https://www.carshop.co.uk/latest-news/cars-with-3-isofix-poi...

There isn't a single compact car on the market which fits a family of five - three children in ISO-fix seats and two adults in the front.

You need to look at the Peugeot 5008 or larger MPVs if you want that.

It's a gap in the market, I'd kill for a Model 3 sized car which was 5cm wider and had three proper seats in the back.

Source: the last three months researching and looking for the smallest car I can buy which can fit the whole family in.

Agreed, there are very few cars on the market that fit the bill. There's the Ford S-Max, Peugeot 5008, and the Audi Q7 (which is ludicrously big) - I think that's it.

It really does feel like a massive gap in the market, and I wonder why that is?

BTW, if you're still looking, and depending on the age of your kids, it might be worth looking at the MultiMac - it's basically a new back bench for your car, with 3x car seats built-in.

I have the Citroën c4 spaceturer which also does this.

The ww Turan is also a option.

Maybe because not many people have triplets? My parents had five children and never had more than one baby seat in the car at a time (they only ever bought one baby seat).

Laws have changed over time. When we got our third our oldest was 6. She was still required to be in a kid seat.

Most of those have the "third" set of mounts in the front passenger seat. Is it common to put kids in the front seat in the UK?

In the US kids who are small enough to need a car seat aren't going to be in the front (air bags aren't designed for kids)

I don't know if its a legal requirement, but every car with passenger airbags I've ridden in over the last five years at least has had the ability to disable the passenger airbag, and clear warnings that you should do so if a child is in the front seat.

A lot of those cars arnt compacts. Something like the Grand C4 Picasso is SUV size. And for the compacts they say:

ISOFIX points can be found in the outer rear seats and in the front passenger seat.

So then you most likely wont have space for the second parent.

The ISOFIX requirement is the big constraining factor. Ditch that and you can find combinations of compact car and child seats which will fit three across, though you’ll have less choice in terms of child seats.

Even if you ditch the ISOFIX requirement, it's still difficult to find a combination of 3 car seats that will fit across the back bench, even with large cars.

No kid who is small enough to be in a car seat should be in the front passenger seat.

And the space. I doubt any normal family car I've ever driven could fit a rear-facing baby seat behind a tall person in the driver's seat, for example.