Welcome!
I know exactly how you're feeling (minus the whole family aspect... do my bikes count? haha) and took the plunge for an older Clio.
Though, having sat in a Clio IV, I can say that all the modern conveniences are there and the interior is a nice place to be, especially in comparison to the Impreza's one.
Boot space is a decent size on them, but it's hard to say for a pram, as prams come in the equivalent of kei-car to massive SUV style. You might have to take a pram to pop in the boot to check it out in that regard.
Performance wise, you'll notice the most from the car being about 260kg lighter than the CVT WRX. After all, the RS philosophy is all about balance as opposed to outright power, so you'll probably find the performance more accessible day to day.
The Cup chassis from what I've been reading at the very least, will leave you speechless with how capable it is. I know it has with my Clio III and comparing it to my previous car (2012 Kia Rio, lots of handling mods. Super fun but slow, needed to be worked hard for speed!), the all round cornering was just effortless, so much so, that my favourite section of driving road felt totally mundane while doing the same speed.
Given the Clio IV has the extra beef from the turbo giving low down torque, it'll be quite the nifty unit for the day to day, as well as punching it (to the speed limit, of course... ) through the twisties.
DCT reliability, I feel, is a non-issue provided you treat it like an automated manual. Being a dry clutch, it's always going to be less strong than a wet clutch system, but driving it like a manual will more or less mean trouble free services.
Looking forward to seeing what you get!