Honestly the main change we felt was going from one to two, having three and then four felt no major difference.
The main issue we see with four is car and size. We have a 7 seat Qashqai presently. Seating children in 'the boot seats' leaves no room for luggage [buggy, shopping] to fit in.
As...
I have four 10, 8, 4 and 2. Its hard!
Every day at least three loads of washing, every evening one kids after school club, weekends constant taxi service. - And lets not even start on the food bill!!