As long as they don't mind getting a little wet they should still have a blast. Plus allot of the people run from the parks when it rains. Hello this is FL and the rain normally doesn't last. Mostly Summer showers.
they will be fine.. They have been so many times that they just do what ever they want to and relax after that.. My DS who is 9 has been to WDW at least 15 times. I have lost count