Now I don't have kids, but I hope this will help!
In 2009 we were in
Disneyland parks for about 20 days. And the only day it rained was the
best day in Disneyland, ever! It was cold, and wet, and the park was EMPTY! DH and I NEVER stay at the park all day and always take at least a 2-3 hr break. But since we pretty much had the park to ourselves we just put on ponchos and off we went, for 13 hrs!!
I would warn you to make sure you are wearing waterproof shoes (No cloth sneakers, suede-like boots, etc.) Many girls/women we're wearing those Ugg type boots and their feet were soaked! Most kids around us that we're still having fun we're properly dressed with parents properly dressed as well. The miserable families were the ones without cover for a stroller or dad who was "too manly" or something to wear anymore more than a sweatshirt that quickly got soaked. Gloves are also a lifesaver too. And invest a couple more dollars in the more durable ponchos. The garbage bag material ones don't last long!
Play it by ear and remember like other PP have said, there are many rides/entertainment to be enjoyed indoors. Also, there are counter service places to eat inside as well. Redd Rockets Pizza Port is mostly inside, located in Tomorrowland in Disneyland. In DCA, Taste Pilots has indoor seating, but it can fill up fast. If you need a quick break from the parks, you can also wander over to the Grand Californian and hang out in the lobby by the fireplace and warm up. Whitewater snacks is located in the hotel and if you haven't heard already, has some great food, which can also be enjoyed inside!
Have fun, and enjoy Goofys too!
