We just went in October with a 6 and 3 year old, so here goes.
1. Definitely go back to the hotel for a nap at lunch time. We took sandwiches into the park and the kids ate them on the bus so that when we got back to the resort they were ready for naptime (well, at least the 3 year old was). Even if you get to 11:30 and think they are doing great, go back, otherwise you will miss out on the evening fun due to meltdowns.
2. Double stroller! If you have one you are taking, then great. We rented from Kingdom strollers and it was perfect. My kids don't usually need one and we didn't want to deal with it at the airport. The stroller was waiting at our resort when we got there and we used it so much. It was cheaper than renting at the parks and much more comfortable for the kids, plus they can stay in it when you leave the parks and it was much easier to navigate the crowds with the kids tucked safely into the stroller.
3. We only went to MK so I can't really discuss the other parks, but we spent most of our time in fantasyland. They also loved jungle cruise, buzz lightyear, country bear jamboree, monster's inc laugh floor, and the people mover (at night this is fun). The haunted mansion was a bust, although they loved the interactive queue. My 6 yo loved splash mountain and big thunder mountain railroad. Depending on the crowds you may not need a touring plan. We always started with one, but if it is not crowded then we just let the kids lead the way.
4. We scheduled one day to just stay at the resort and swim, watch the movies under the stars, and go to downtown disney. The kids LOVED this day and there were still things we didn't do, so next time I will probably schedule 2 days to just hang out at the resort.
5. I took a box of cereal, applesauce to go, and other snacks in a suitcase, then we ordered milk, lunch meat, etc from garden grocer. It was nice for the kids to have something to eat right away in the morning without having to go down to the restaurant. It also save $$. We did Chef Mickey's for dinner the first night and we always love it (probably my husband's favorite meal) and since the kids get to see the characters during dinner, we don't have to wait in line to see them at the parks.
6. HAVE FUN!!