I'm soon to have three kids under two years old. I'm comparing the Kia Carnival and the Mazda CX-9. Looking for your recommendation plus any guidance to save money.
Buy the carnival - every time. Four more years' warranty, true annual servicing (Mazda is 12mth/10,000; Kia is 12mth/15,000 - means the Mazda needs servicing every eight months for average drivers.)
More importantly, you can remove the centre seat from row two in the Carnival. This means you can walk through to row three - making it heaps easier to fit kid #3 in a kid seat in row three. Also in the Platinum - power operated sliding doors (a real plus juggling all that kid logistic support stuff). Carnival has head-protecting side airbags for all three rows, too, so the child in the back is not a 2nd-class citizen on safety. (CX-9 has this critical head protection as well.) Read more Kia Carnival Review >>
Mazda has a space-saver spare. (Limited to 80km/h - not much fun on the freeway in the rain.)
Carnival is eight seats (so removing centre seat of row two still yields seven viable seats. It also has four child restraint anchorages points (outboard positions in rows two & three) of which three (I think) are also ISOFix compatible.
Carnival also has viable luggage space with all seats deployed. CX-9: not so much. CX-9 is certainly more fashionable; Carnival is certainly more practical for standard family duties, Cracking diesel engine in the Carnival too.