Water parks, there is also Aquatica to consider. It's much newer than Wet'n'Wild.
Everyone does seem to rave about Discovery Cove and it counts as pretty much an active rest day.
I wasn't that fussed about SeaWorld last year, I was very disappointed with the Polar Bear display. Many of the animals were displaying that psychotic swimming exactly the same path again and again behaviour. You get that a bit at Animal Kingdom too, but it was really noticeable at Seaworld for almost all of the marine mammals. Most people seemed to think it was great, you knew exactly where the animal was going to swim up to for the photo opportunity. Ocean Park in Hong Kong does the seals and penguins much better. Also considering the ages of your children, SeaWorld seems to be going a bit for the thrill rides, like Manta. Lots of height restrictions to consider with those.
Don't forget Tampa isn't far to the west coast and Busch Gardens, again, a bit more thrill ride, but they do have a lot of other stuff you don't find in Orlando, plus you see the other side of Florida
. The combined tickets with Universal and SeaWorld (Orlando Flexi Ticket Plus) make it a pretty cheap add on.....
Staying on property, you can get the tickets for length of stay, and if you do that they sometimes include meals, probably not with the F&W at the same time though. It depends on how the US economy is going next year. Length of stay tickets give you the extra day at the end, with park hopping etc. Park hopping is worth it for Animal Kingdom, go as early as possible (the one park where I will use EMH) the animals are more active, by midday, they are having a nap, so you can then go to another park, though with the queues for Expedition Everest, that could keep you busy all day
I usually do AK in the morning and Hollywood Studios in the afternoon/evening. Don't miss Toy Story Mania! regardless of how long the queue is 
MNSSHP is a separate ticket, so you could do that one 'rest day' the week you are off property, you can get in from 4pm for a couple of hours Magic Kingdom without the themeing and then they roll out the Halloween stuff while you are in there. I wouldnt waste a ticket on a park during the day and then try and stay out for the whole MNSSHP.
Everyone does seem to rave about Discovery Cove and it counts as pretty much an active rest day.
I wasn't that fussed about SeaWorld last year, I was very disappointed with the Polar Bear display. Many of the animals were displaying that psychotic swimming exactly the same path again and again behaviour. You get that a bit at Animal Kingdom too, but it was really noticeable at Seaworld for almost all of the marine mammals. Most people seemed to think it was great, you knew exactly where the animal was going to swim up to for the photo opportunity. Ocean Park in Hong Kong does the seals and penguins much better. Also considering the ages of your children, SeaWorld seems to be going a bit for the thrill rides, like Manta. Lots of height restrictions to consider with those.
Don't forget Tampa isn't far to the west coast and Busch Gardens, again, a bit more thrill ride, but they do have a lot of other stuff you don't find in Orlando, plus you see the other side of Florida

Staying on property, you can get the tickets for length of stay, and if you do that they sometimes include meals, probably not with the F&W at the same time though. It depends on how the US economy is going next year. Length of stay tickets give you the extra day at the end, with park hopping etc. Park hopping is worth it for Animal Kingdom, go as early as possible (the one park where I will use EMH) the animals are more active, by midday, they are having a nap, so you can then go to another park, though with the queues for Expedition Everest, that could keep you busy all day


MNSSHP is a separate ticket, so you could do that one 'rest day' the week you are off property, you can get in from 4pm for a couple of hours Magic Kingdom without the themeing and then they roll out the Halloween stuff while you are in there. I wouldnt waste a ticket on a park during the day and then try and stay out for the whole MNSSHP.