Gotta agree with Mark5.
I have a Clubman but waited until my youngest was a toddler and can climb in himself. I choose the Clubman as it still a Mini but with a rear door & I just dont like the look of the Countryman.
ANY 3 door car is a nightmare trying to get kids in/out and even if your pram fits in the boot (physically check this at Mothercare before you buy a pram as 90% wont fit a mini ), & it means you have no boot space left.
Of course you can compromise on these issues if you really, really love your Mini, & many people do.
But the fact is the Mini was never designed to be a family car and so many other cars do that job so much better. But theyre not Minis
Personally I would recommend you move the Mini on now and buy a 5 door Golf GTI - before the arrival of the baby as believe me you wont want to be tyre kicking with a new born. Then in 3 years time, you swop the Golf for a used Mini
JCW F1