As others have noted a RAV4 has quite a bit more more luggage space than a CX5 and would be the direction I went if I wanted 2 kiddy seats and space for a stroller whilst still having room for shopping and the like. A CX3 is out because it has almost no boot space, a CX30 will be too small for what you're trying to do, but will be better to lift kids in and out of than a Mazda 3 as it's higher off the ground.
Note - my better half works for a Mazda dealership and has had pretty much everything in their range as a drive car over the last few years so I have actually driven them extensively, and my vehicle is a RAV4. You should see better than 8l/100km from a 2 litre non-hybrid RAV doing the Auckland commute and better than 6l/100lm in a hybrid one.