I find it small. I haven't tried to fit a stroller back there as we don't use the back row very often, but it seems tiny.
If you don't have this car yet, I would think hard about it. I bought this car in order to have extra seats. We only have 1 child but we also only have 1 car so I wanted it just in case. It does come in handy but if you are thinking of putting several small children in car seats in this car, take a closer look. It is technically possible to fit 4 car seats in this car, but it takes a lot of finangling.
if you have car seats in the middle bucket seats, the Mazda manual REQUIRES you to have the seats pushed all the way back. That makes it impossible for a person to sit in the third row behind that seat (although you might be able to fit a car seat).
Take a look at this video from Car Seat Blog. It shows the space accurately.
[ame="http://www.youtube.com/watch?v=nGTNn3Rf_7w"]2012 Mazda 5 Kids and Carseats Review - YouTube[/ame]