There are actually lots of things to do at the parks that are not specifically "kid" oriented. At MGM there are TONS and TONS of characters they will know from the more recent movies, Playhouse Disney, Little Mermaid, the Muppets, etc. My 2 and 4 year old love the backlot tour because they get to ride in a tram (yes - I am sometimes tempted to ride around the MK parking lot all day to see if they ever tire of the trams

) and of course Fantasmic. At EPCOT there is the Living Sea (in which most of the attractions are based on Nemo including a new one where Crush is interactive and answers questions from children) and Imagination where you still get to met Figment and play at the end (sound boards on the floor, areas where you can make Figment play instruments by moving your arms through an open area surrounded by sensors - pretty fun on a hot day especially) and Innoventions where they can play and touch things. Animal Kingdom and Magic Kingdom are mostly for the smaller kiddies but make sure you read about the rides in a guide book or ask a Cast Member what the ride entails if your children might be sensitive to lights or loud noises. OUr first couple of trips, we stayed away from things like Goofy's Barnstormer to make sure they didn't get ridephobic, and now that we have ridden it once, all they want to do is run back through the line and ride again. You know your child best. If you are unsure of a ride, either you or your hubby preview it alone first while everyone else gets a snack.
Do drink lots of water. Do get up early enough to get to the parks when they open. Lots of people don't and by the time they get up and have breakfast, you will have ridden 3-4 rides and be ready for a break. TAKE BREAKS! You don't have to do it all in one day. If your children will sleep or at least be quiet, then there are lots of quiet places you can pull your strollers to in the shade and take a rest time (I am so lucky in that my boys will sleep when it is nap time no matter where we are so we just get a cold drink and let them sleep and people watch - that way we ALL get rest) or go back to the hotel, have a bite and take a nap. Let everyone else sweat it out in the heat of the day while you are recharging!!! The pools are fantastic, but I will admit we rarely take the time to use them. Learn how to use the Fast Pass system and NEVER be without one (unless somehow the parks are not crowded for that day!). If you want do to Character Meals, call 90 days out and book them. (big hint here - if you can get into one before the park opens then you will have a chance to do things like take a picture or two of the castle with no one there and you will be ready to ride when breakfast is over). Take the minimum amount of stuff with you into the parks. Sunscreen, sunglasses and hats will be a must as will diapers, water, snacks, etc, but if you think you can get by without it DO! Those bags get so heavy by the end of the day and even if you have a stroller to help haul the load, you will end up standing with it all in your lap or on your shoulders on the bus back to your hotel and that is no fun! Take multiple pairs of shoes for each person because it does rain there often and wet shoes the next day - blah!
We don't plan too specifically for our trips other than usually one Character Meal and which parks which days. I do offer my children choices about rides and if they want to meet characters and they know that sometimes things change when we get closer and see the line, etc...so all of us being flexible is the key. One thing we do (and its a bit of bribery and a bit or reward all mixed in one) is go to Downtown Disney before leaving and let them pick one thing from the
Lego store. This keeps me from needing to buy LOTS of souvineers because I remind them that they will get something on that day and it also helps me to remind them that I need good behavior when we are in such a big place. They love that store and your 4 year old son probably will too. There is a HUGE playard full of legos and play equipment (its free) there that keeps my 2 boys entertained for a while and allows me to stroll and shop while hubby keeps and eye on them. A last day treat for us all.
Hope you have a blast!!!