you could realistically use any large saloon or estate car, aswell as the obvious MPV's...
i dont have 3 children but i do often carry 3 or 4!
I currently have a vauxhall omega saloon, really comfy car, tons of boot space for prams and whatever, aswell as loads of space inside (my neice looks lost sittin in the back when i pick her up from school lol), and its quite a safe car. downside of mine is running costs if you're only doing short journeys (2.5 V6 petrol), and tax etc, and parking if you arent used to bigger cars.
my sister drives a renault megane scenic... im not a fan personally (mostly because its french! lol), but it does have plenty of room for the kids, and the amount of stuff she seems to carry in it is quite surprising lol not sure what its like for running, but i do know its only a 1.6, which in a big heavy car usually means crap fuel consumption too (as you're always having to accelerate). pro's are the space and also the felxibility of being a 7 seater (though you're compromising boot space then). seems to tick most of the boxes. though i do find it a complete pain to drive with its automatic handbrake and crappy clutch.
My brother and his fiancé have 5 kids between them, he currently has a ford focus C-max, which jus isnt big enough if they have all the kids (in which case he uses the transit mini-bus! lol). hes currently looking at an S-max, 7 seats, tons of space, decent spec'd car with a few engines to choose from based on what you're after... though i havent driven one yet, so cant comment on that.
Dad's got an audi a6 estate, 1.9tdi so econimical enough, nice comfy car to drive, plenty safe, and loads of space being the estate version. can fit the 3+ kids in the back no problem (though its not quite as big as my car). downside would be any work needing done - audi arent cheap!... but there is less work to be done, so proves cheaper in the long run that a crappier car lol
erm.... all of them i drive regularly with the kids in, though i dont have to "live" with them, so thats all based on my personal experiance and whatevers came up in conversation with the owner of whichever car.