I have a VW Touran which is pretty good. 3 child seats in the back no problem and then an extra 2 seats in the back if needed. They are really easy to put up and down, and its amazing how they disappear into the car (ie you dont need to take them out or anything). The boot still isnt as big as an estate boot though big enough. When all the 7 seats are up it is small!
One issue is the running costs of 7-seaters - I did my research on www.nextgreencar.com - you can search on car type and see the road tax, co2, fuel per mile etc. There is a real difference in running costs dependent on what specific model you select.
Hope this helps

MM