Check Disney's website for what parks will be open what hours. Get to Hollywood studios early - like before it opens so that one of you can run to get Toy Story fast passes because you don't want to miss it and probably don't want to wait an hour. Use your waiting time to see the other things. Star Tours is going to be packed so make that your second Fast Pass and do everything else as walk in. Don't miss the animation studio when it gets hot. It's cool in there...there are characters and if you think your kids can sit still there is a free class where you learn to draw a character - great free souvenier!
Realize that it's going to be hot, you aren't going to see everything...it's okay. Making what you do see enjoyable for you and your kids is what makes memories. It's okay to leave something to see again. It's so easy to get wrapped up in running around so plan a little down time at the pool or just crusing on Disney transportation around the lakes near Magic Kingdom.
In MK - go to Fantasyland first thing in the am. Get it done, then head for fast passes at the coaster of choice. Take a break mid-day and go back to the room to swim and rest or relax a bit.
Animal Kingdom - The safari ride can Fast Pass out so that's a must get early, but it's also in the back of park. Everest can be rode as single riders depending on how young your kids are. Pack bathing suits/flip flops for the water ride. Schedule time for your kids to play in dino land and enjoy a cool drink with hubby while they dig for dino bones in the shade. A great break in the middle of the day - plus the restaurant near there has refillable drinks.
EPCOT - The countries are perfect night time activity. Don't miss the KIDCOT stations for the kids. Innoventions at the front of the park is open until 7pm and is a great place to spend some time when it's hot. Lots of educational/fun activities. Must get Fast Passes are Soaring, Mission to Mars (can single ride) and Fast Track (can single ride). If you have time the Kim Possible Adventure makes the countries more fun for kids and adults.
Have fun, don't stress! If you have any specific questions you can PM me. We are passholders and have been there hundreds of times.