My cousin has ones and loves it, but yep, its not very suitable for too many kids.

They find it v hard to get some into the back seat, climbing over the car seats in the middle row, esp hard for bigger kids and adults.
If you have a couple of car seats, it becomes v small, with little boot space left for prams and/or shopping too...

To fill it all up completley i think you may find it way too small.....