Make sure that you run the numbers before you decide to make changes. The Kids Play Free offer might actually be a better deal for you. With two kids under the age of 10, you're looking at saving $658 on 5 day base tickets for them (more if you have hopping, waterpark fun or more days). Compare that to the $94 per night you would save with
free dining at a value resort (or the $116 per night for moderates or deluxes).
If it does turn out to be a better deal for you, then you can change your reservations as long as you are not closer than 45 days until your arrival and there are rooms available where you want to stay.