I've had 2 MINIS over the last 3 years and my 2 boys are now 6 and 8 - they fitted fine in the back but its getting tight now with the younger one behind me. I probably have another year with the R53 before I need to move to an R56 of some sort (Or maybe a Clubman) for the extra few inches of Legroom.
As for boot space, well we did a week long trip with the 4 of us over 1800 miles and we coped - you just have to be very selective about what is "essential" for your trip!
