I have two kids aged 5 and 3.
We had narrowed our choice down to Honda Jazz and Audi A1. I can't remember why. A lot of whittling. My husband was obsessed with the idea that the Jazz was for old ladies and we went out spotting A1s and Jazzes and the latter were always driven by old ladies. Not that there's anything wrong with that. I wanted: a panoramic roof, lots of airbags. He wanted: not to look like an old lady. The Audi was more expensive but not a *lot* more expensive. After I test-drove both, the choice became pretty easy. The Honda was very slow to accelerate and felt plasticky throughout. The Audi was nippy and felt solid and expensive. That was how we chose.
Since then, more practicalities have come into play. There's a problem with the front seats not easily locking into place, so I can often squash a child's leg when I'm trying to get it to lock, as it has to go all the way back. It is easier to get the kids into my mum's mini, there's more space in the back - no kidding! - and the seatbelt ports are more easily accessible. There are only two seats in the back, so there's just no issue of being able to squeeze in between with car seats there or not. (We used to drive a Yaris and I could squeeze between two skinny seats, but I've been in a huge rental Mercedes saloon and there was no room at all between the same car seats.)
The boot space is small. Smaller than the Yaris, bigger than the Mini. It will hold a Maclaren buggy but not a bigger one. The Yaris took all sorts of huge buggies, but we're done with buggies now. I think, in fact, thinking of the Yaris now, that the Yaris was much easier with kids. And that was not un-nippy (though less so). This looks a bit flasher than the Yaris. It is more fun to drive. But the thing with the Yaris was the new one didn't seem as good as the old Yaris, it had worse reviews, the new gimmicks (the wireless features etc) seemed like a waste of money.
The kids love the sun roof, so if you're going for this, get a sun roof. The kids are perfectly happy with the car, and my husband is a little over 6'3", so one of the front seats is always pushed right back. It's close to their legs, but so far it works.
It's a new car, so I'm not expecting it to go wrong, and indeed it hasn't. That front-seat click thing is really annoying. We also drove a Golf for a while and the mileage is ridiculously better with the A1. It scored very well in child in the back safety tests. What else? The stereo sounds good, we got the basic one. I like my car.