Remember to roll up your trousers legs!! esp jeans , nothing worse than them even slightly hitting the heel on your shoe they will slurp up the water and it will work its way up to your knee before you know it!!
This is a must! It rained twice when we were there and the first night I was wearing waterproof boots and a poncho but didn't roll my jeans up

didn't think of that

. And my legs, up to my knees were drenched! And I got very cold because of it.
The next rainy day I noticed so many people and children walking around with soaked legs up to their knees.
Anyway the first night, when it was wet it was sleet and it was horrendous. It was freezing cold and windy, we had soaked legs (dry feet

), were wearing poncho's but the sleet hitting us in the face actually hurt.
Next wet day, better prepared, no sleet, kept dry under poncho and much more pleasant, just kept to the arcades, rides under cover as much as possible. We did have a damp morning another morning, but didn't even wear ponchos that morning, it was just a light spray that came and went so wasn't too bad.
So, wellies are a fantastic idea to keep your legs dry (and warm) and a poncho or raincoat, its still fun in the rain, it's
Disneyland 
.