Rates for Children under 2

I've been searching around all kinds of websites and this one seems the best! Thanks for all the great info. Something I read on the website is that Carnival offers free sailing for children under 2. Does anyone know if this is specific to certain times or certain ships? We are booked on a cruise next month on Carnival Triumph to the Western Carribean. Both Carnival (when we called independtly) said there are no discounted rates for children (meaning, everyone has to pay same price). Our travel agent also said that there are no discounts for smaller children. My 21 month old (next month) will be coming with us and was charged as the 4th person in the room, so I knew it wasn't fair and discouraging me from going.. because it is very expensive.. especially since she will not be able to participate in the children's activities and swimming and will hardly be of cost for much of anything on the ship. Does anyone have experience with this? I think I am being ripped off!! But my brother is getting married on the ship and everyone is cruising afterwards, we can't miss it! So I don't know what to think and I don't want this to ruin our trip. By the way, this is our first time cruising, ever. Help is appreciated!