Hello H.,
I also took my son on a cruise when he was 26 months old. It was a big party with our dear friends and in-laws for a 5 day New Years cruise. He was old enough to use Club Carnival so we tried. After awhile he figuired out we were haveing fun without him and would start to throw a fit and we would get a call to pick him up. We did use the babysitting service too, but he kept doing the same thing with starting to cry and becoming so upset that we would get a call. One thing we learned quickly is no matter what, whoever drops him off MUST pick him up. The first time my husband went to pick him up after I dropped him off was a pain because he was there throwing a fit and could see Daddy but Daddy couldn't take him. My husband had to come get me to pick him up.
They were very accomidating for dinners, which is only appropriate since we spent just as much for his ticket as for our own. When we were having lobster he would have mac and cheese! It was funny, but there was no way he was going to eat the gormet grown-up foods. It was way cool that we could order peanut butter and jelly any time we wanted or needed through room service. We also were able to get the Soda pop band for him and the rest of us to use as needed. One thing that was challenging was that he was still on a sippy cup so we had 3 that we just kept washing in our bathroom sink. I would suggest the throw away cups so you wouldn't have to worry about that.
He was also a big pacifer baby and we had brought several with but the 3rd day when we went to Mexico we lost our very last one as we were getting back on the boat. He had finished his drink and we were very conscious of not losing the last pacifer so we stuck it into the cup. Just as we were getting everything together to board the ship the cup and last pacifer rolled into the gulf! We were beside ourselves. There was no where on the ship to buy a new one and our son would not sleep without it. We actually paid another passenger $6 for one of his daughter's. It was the best money spent the entire cruise! So I guess the moral to the story is if your little guy is dependent on anything to sleep or comfort himself make sure you keep a VERY close eye on it AND bring more if possible!
The other thing we did was take advantage of was the portraits they do all the time on the ship, as family photos, with Mom or Dad with our little guy, and by himself. I think that is where we spent a LOT of $$.
All in all, it was a very expensive trip to take with a little guy that will never remeber it. The pictures helped because we talked a lot about it with him after the trip was over, so he kinda knows he went. If that is not an issue with you, then I think it was an awesome time for us to have to spend with our little man!
Just one more thing to add, I don't know if you have been shopping prices, but we were able to get a killer deal through Abracadabra Cruises. Their website is http://www.cruisemagic.com/
Good luck on your decision!
J.