I just wanted to say that my husband and I took a cruise a couple of years back with our two small children. They were 2 and 4 at the time as well. It was a 4 night cruise into Mexico on Carnival. The kids actually did fantastic. My 4 year old cried at the end because she didn't want to leave the ship.
We did send them to camp Carnival a few times and they really enjoyed themselves there. There never seemed to be any problems with Camp Carnival. We as parents were a little nervous leaving them, but we would sneak up to check on them, and each time they were playing have a great time. So no real issues there.
I guess there are really numerous pros to taking the little ones with you. As for cons, of course you as parents are somewhat limited on what you can and can't do, mostly at night. Babysitting can add up real fast. We didn't mind turning in early because we too were tired by then. Or I would go in early and my hubby would go to the casino or find something to do. There are ways of working around everything. I guess it's just a matter of how much alone time you and your husband want. We went with the notion of spending time with our children.
All in all it was great fun. Formal night was really cute with the kids being all dolled up. And in Mexico the girls shopped, got their hair braided, and had a good time. I have read that you can actually go to some of the local resorts at ports and eat, swim (some with kiddie slides and play areas), hang out, for a fee of course. But that's an option at the ports. Transportation at the ports is something you may want to think about. Some of the taxi & bus drivers drive crazy and they don't necessarily have car seats for the little ones. We didn't put our children in any vehicles while in port because we were there for such a short time, we walked. But that is something to think about.
Best of luck on your decision making. I hope what I wrote helps a little. We are actually taking another cruise next week for 8 days into Mexico on the Carnival Spirit and taking our girls again..........only now they are 7 and 5. We are all looking forward to it