Regarding adjoining rooms, on our last cruise with the kids (much younger than yours) I found it way less expensive to book two side by side rooms with a door adjoining them than to book one larger suite that would fit all of us. That way it gave both the kids and ourselves a little privacy and plenty of room.
One thing to consider though, if it's important to you, is that your level of service and some of the perks you get by booking a suite will be better than any other room, no matter how many you book. One big example is that I hate lines. I hate waiting in them. On Carnival, if you book any room at the suite level or higher you get priority boarding, priority tenders off the ship (in places where you don't dock), and priority disembarkation when returning. The day you arrive, instead of waiting in a long snaking line for hours, you get to walk right through and into a nice office for one on one attention from someone to check you in.
For way more information than you'd possibly ever want, check out the Cruise Critic boards. Just like here, search is your friend over there and anything you can imagine has been asked and answered!