I know this is a really late response (have only been on MN since November) but I have cruised with Carnival three times. Where in the Caribbean are you going? I've been there a couple times and may be able to give you pointers on which excursions are good and worth the money.
They're pretty good, I don't have any complaints. As for tips, if you plan to do excursions, book them as soon as you can as they tend to book quickly. Whatever you do, NEVER book excursions with people hawking them in the different ports as they will more than likely rip you off and they cannot guarantee to get you back to the ship by the time you need to be there and the ship waits for no one. If you miss the ship you are on your own to fly to the next port and get back on then.
The food is all inclusive (as you probably already know) as are most of the non-alcoholic drinks (aside from sodas). Becareful when having drinks or buying things on ship as it racks up quickly and you don't realise how much you've spent until you get the bill slid under your door in the early morning hours the day you come back and take it from me, it can be a rude awakening.
I know they have a kids camp of sorts on board though we haven't cruised with the kids. One of DH's former grad students and her husband take their kids on cruises as vacations rather than traditional vacations. She says it pretty much works out to them saving money and the kids love it.
hello,myself husband and 2 dd's 13 and 4 will be cruising out of miami for 2 weeks on the carnival glory in feb 2011(2 weeks carribean). has anyone cruised with carnival before?any tips experiences etc would be gratefully recieved,thanks