I have a Yaris - I love it, but it certainly isn't roomy.
Pros - it is hugely maneuverable and easy to park which is a huge blessing in the city. It's pretty fuel efficient but not so lightweight you feel vulnerable.
Although it is short, it is quite tall for a car of its category so you can fit in quite a bit if you don't mind piling stuff up and not being able to see out of the rear window and have a packing strategy such that your piles won't collapse on top of the DC. There's also quite a bit of space in the footwells under the DCs feet which will take 3 or 4 airport-carry-on type bags.
We can quite comfortably fit 2 adults, 2 kids in car seats and enough stuff for us to be away for a holiday, including a travel cot. Having a smallish car does encourage us to be strict with ourselves about how much junk to take of course. However, when we went camping and needed there to be room for a tent and various additional items of out-door equipment, my DH caught the train so we could fill up the passenger seat volume with stuff. We debated whether we ought to be getting a "family" car at that point, and concluded that it wasn't worth paying for the additional petrol to power an extra half-ton of additional metal during the 99% of the time when we don't need the extra space, just so as to avoid this kind of inconvenience 1% of the time.
So I guess the question will be how often will you go camping?
I've never owned a car or even really driven one. Got my driver's license years ago and haven't driven since but want to get a cheap, secondhand one now since with the kids I feel like it would sometimes make life easier and increase the amount of stuff we could do. We've got a 1y.o and 3.5y.o. Live in central London so wouldn't be using this daily, it's more of a weekend trips/errands type car though it might also be nice to use for longer trips.
What I'm wondering is: am I going to regret getting a Yaris instead of say, a Corolla, and always be wishing I had more space or will I be happy to have a small, maneuverable car, especially given my lack of driving experience?