Car wise, its not just having 2 cars or a 7 seater thats the issue. We will get another car down the track, but this is how i see it. If you have 5 people in the family, then you can have the big car (like our 7 seater) and then a smaller to mid range car as the 2nd one, because 5 people can still fit into it. (for eg Mels brother and his wife have 3 kids, and they have a larger people mover style vehicle, and then a Toyota Echo as the second, and they can fit in that (tightly though).
If you have 4 kids, I see you then need two 7 seaters, cos I feel it is pointless having another car that cannot transport everyone in the family.
Why not just get two 7 seaters?
Cost, and also, when we had 2 cars until recently, 1 of them hardly got driven (like once maybe twice a week?) so it is hard to justify the extra cost of a big costly 7 seater for not much 'drive time'.