Let me tell you, Atlantis is amazing!
We were there on our cruise a couple of years ago and we absolutely loved it, both the kids and us. We had kids 10, 6 and 3 and everyone had a great day. Think we had to pay a little extra for the 5th person but wasn't much if I remember right.
We actually booked the day seperate from the cruise as we had insight from a fellow Dis Meets member. We booked a room for the day and luckily got a great rate (don't know if that would happen everytime) but we got a room for about $140ish. With the room everyone has access to all the hotel amenities including wristbands to the waterpark, which is amazing, and then you have a place to leave your stuff, get changed, etc. You can get a taxi to there and we luckily jumped on a returning shuttle taking other guests back to the ships for nothing!
Food is good but extremely pricey and you can probably get away with bringing something in your bag to eat.
We are going back on a Disney Dream cruise in Feb. 2011 and doing a back to back 4 day/3day. Everyone wants to go back to do Atlantis both trips back to Nassau. They have a Lagoon and an aqarium with a variety of sea creatures including sharks. They also have a place to swim with the dolphins but when we were there the water in the lagoon with the Dolphins was so murky you wouldn't have seen the Dolphins until they were right next to you. If you were interested in doing this I would check out the conditions first before paying the $ to do it.
We did book a Comfort Suite room to begin with but we kept checking for deals at Alantis and when we found the final deal we went with and it turned out cheaper than Comfort Suites, which we then cancelled.
I highly recommend taking in Atlantis, you and your kids will have a great day, providing the weather cooperates, of course.
If you have any more ? I would be glad to answer them.
Gord