Hi Steven,
Here's what I would do:
Try to get an early breakfast reservation at Cinderella's Royal Table. Those with early reservations get to enter the park before it opens. Your daughters will feel like VIP walking past all the normal folk waiting in line for the park to open. All you will need to do is give your name to the castmember at the front of the gate and, of course, obtain the very sought after reservation. You will need to call (407)WDW-DINE in advance.
Then I would take them over to the Bibbidi Bobbidi Boutique ((407)WDW-STYLE). They might not want to get dressed up like a princess, but getting their hair and nails done inside Cinderella's Castle will be memorable. Some not to be missed attractions at the Magic Kingdom would include, Mickey's PhilharMagic, It's a Small World, Pirates of the Caribbean, and Monster's Inc Laugh Floor. I would also try to see the Dream Along with Mickey show that takes place in front of the castle. The show's times will be listed on hand outs that can be found as you enter the park.
After doing the best of the best at Magic Kingdom I would recommend visiting Hollywood Studios. Your girls may enjoy one of the live High School Musical 2: School's out shows. There are also other great shows and attractions. The biggest and best being
Fantasmic. You will all be very impressed by the great storyline and awesome effects. It's truly magical to watch.
Other than that, leave time in your schedule for them to make suggestions.