I own both E90 M3 and E92 M3, and both are very spacious.
Love the cars, I used to go to the track every weekend (Sundays and Mondays)
Now, I'm not married and I don't have kids.
But IF you really don't have to take your children that often, go with the 911 Carrera S..
You will love the car..
and between M3 and C63, take the M3.