1st - don't believe all the people who will tell you, "It only rains for 20 minutes!" There is no magic weather umbrella that prevents longer rains...especially in rainy seasons.
I plan every morning as an "in the parks" morning. It does rain all day sometimes, but mornings are usually okay.
We have done parks in the rain, but generally when it is raining hard, we leave.
We've gone to many a dinner show, seen the Titanic experience, the upside down house place, etc.
The big McDonalds is a nice experience - they have a pasta bar that isn't bad and is really good, considering it is McDonald's.
One August we had 9/10 days of rain. Doesn't always happen, but it can. DS bought a Mickey pin in a yellow poncho because he felt it was an apropos souvie for that trip. Almost all those days were "rain for hours" kind of rain.
You do your best!
Bring extra shoes. You can try that "fill them with newspaper and they dry overnight" thing, but it only works for some people (not me.) An extra pair won't hurt.
Good luck and have fun!