I have an MCS - not the Clubman - plus a 6-month old and a 5 year old, and never have a problem either. And it's our only car. Some people just like to worry about things like that, on their way to convincing themselves that they need an MPV or a Chelsea tractor.
Though I am swapping for a Clubman later this year, as the MCS is now ancient and a bit more space won't hurt. The club door is on the CORRECT side IMO - I can guarantee that as the driver, I'm going to be opening and closing the driver's door a lot, and having the club door on the same side makes perfect sense; if it were on the passenger side, I'd need to run round the car every time that I wanted to use it (so probably would end up not bothering!).