Re: now don't all have a go but..
We have a 156 and a 164 and an MPV so I can give my views on all three for what they're worth!
Firstly, to answer Wrinx's question, when I was a kid, our family of 5 used to have a Reliant van as our transport. We three kids used to just sit in a big pile in the back. Eventually, my mum and dad scraped together a bit more money and bought it some side windows and a rear seat. So of course it's POSSIBLE. It's just not NICE.
These days, however, it's against the law to put kids in a big pile and leave them to get on with it. Has anyone tried putting three forward-facing child seats in the back of a 156? - or even 2 forward-facing child seats and one booster cushion? It ain't easy! We have managed to get the pram into the boot of the 156 but the seal is ragged to hell because it's a tight fit to say the least. Also, our 156 is too old to have "Isofix" kiddie seat anchorages or a three-point belt in the middle rear seat.
The 164 is bigger (wider mainly) but not that much more practical. The kiddie seats don't strap in particularly well because the rear belt anchorages are in daft places and again, there's only a lap belt in the middle. It has a much bigger boot though but the rear springs are such that it just sits on its bump stops as soon as we put a packet of nappies in it! Besides, the seats are leather and the kiddie seats aren't kind to it!
I am lucky enough to have a Peugeot 807 as a company car (although Gordon Brown does very well out of me for the privilage)! I have to say that as a "mobile living space" this really excells. The French know how to do "family travel" and there are lots of nice touches - little kiddie mirror for us to see all the rear seats at once, "fridge" compartment for putting babies' bottles in on long trips, sliding doors so that when all the parent & child spaces in the supermarket are taken up by "cashpoint cripples" we can still lift a rear-facing kiddie seat through the doorway - even when parked between two cars. (VERY important, that!). All the seats lift out so it can be a van (and has on many occasions)! Each brat has its own seat and we can get to the belts because there are three rows. We can take other peoples' brats (sooner or later, your kids will make friends with other kids!) along to various activities. Up to about 6 years old, the kids can stand up full height and walk round when we stop for a butty. The seats all turn into tables / cup holders & so on....
The downside? well 32 MPG average (it's the 110 diesel) and frankly, I don't think Peugeot's slogan of "the drive of your life" is entirely appropriate! But it will sit at 80-90 all day on the motorway quite happily. Other downsides? IF we fill it with people it has NO (zippo, zero, nada) luggage space - you'd need a roof box for that and the MPG will take another hit. Obviously, if you're not using all the seats, you can take one out and have plenty of space but everything is on show when you park the car up. Also in a big smash, you'd have to suffer the possibility of getting rogered by the folded up push chair and whatever else was loose. FInally, I'm on my 5th and all have given some degree of truoble under warrantly (always electrical). The Citroen C8 is identical (built on the same production line) and generally cheaper so if you don't mind the build quality, you get the same faults for less money with the Citroen.