No way we could get 2 seats in our small 1-Series. While it's fine for my wife when in the passenger seat with the child seat behind her, the drivers seat would be far to forward if we were try to and fit one behind me.
If you're talking about the BMW 1-Series this has a peculiarity that most small cars don't have: a rear wheel drive (or all-wheel in some models) and a longitudinal mounted engine. This means substantially less space inside, especially in the back with the higher floor and the drive shaft down the middle. I found the Polo a lot more spacious than that.
I second that! VW Polo and two kids work - despite being able to buy about any car there is, we stuck with a Polo until last year. All our gear was bought to fit in it. It is possible to find small stuff that fits. People who say stuff for two kids does not fit in a small car have not thought about it long enough or should seriously consider what their "needs" are.
Buy smaller strollers that are easily foldable, instead of bulky ones. Buy smaller and softer bags so they can fill every gap. Buy car seats that are a bit less space taking.
The only time we were in a bit of trouble with space was when we went on a big vacation with 4 people.
But that happened only once (admittedly, we usually takes flights when going on vacation).
You can fit two car seats in the back of mine as well -- but only if the parents are both under 5'6" tall and happy to have the front seats as far forward as they go.
My car isn't one of these modern, ever-growing ones, but it's not particularly small in most respects either.
American car seats are huge. A friend of mine, who is not small – even by American standards, despises SUVs and ended up having to import a car seat from Japan for his spawn.
I’ve been wanting to buy a European car seat but am worried about the legality of it. I can just imagine my insurance company refusing to pay for injuries because the seat doesn’t have the right stamp on it.