The pool at the Port Orleans Riverside is fab, our kids (2 and 4 at the time) loved it. I would second ccbb's advice; up and out early to parks for opening and back to the hotel for a rest in the afternoon. We 'did' a park in the morning, had lunch, went to the hotel for lie down/pool, out for tea and another couple of hours at a park, possibly a different one to the morning.
Our kids loved the Disney evening fireworks/parades (we went back to the parks in the evening).
The Buzz Lightyear ride at the Magic Kingdon was a winner. The Animal Kingdom has a great playground in the dinosaur bit where the kids can go digging for bones and adults can sit down (in the shade)!
Typhoon Lagoon and Blizzard Beach are defnitiely worh visiting and both have great areas for children. I think you can go an hour earlier than opening if you stay at a Disney hotel. Our dc's still talk about these a year later.
I made reservations (priority seating in Disney speak, I think) for everyday in advance. If you decide not to go it doesn't matter, if you do, you have priority over people who haven't booked.
There is less for that age group IMO at Epcot.
They loved the Whispering Canyon Cafe restaurant at the Disney Wilderness Lodge Hotel (we parksed there, ate and got the boat to the MK in the evening). Boma at the Animal Kingdom Lodge was great too.
Hope you have a great time .