Before I get into describing how beautiful our Florida weather is, let me make something clear: unless you are in Orlando during the few cool times of the year, you need to drink a lot of water. Avoid sodas, especially with caffeine in it. I am not a doctor, but every time we have brought someone to the parks whom did not drink water regularly and went for sodas instead, they ended with mild dehydration symptoms. It happened to my nephew, my mother and other relatives who drank only when they were thirsty. In warm to hot weather, at least here in Florida, you can lose fluids so fast the body does not have a chance to trigger a thirst response quickly enough!
Also, make sure you bring sunscreen (even in winter). You will be walking around all day, mostly in sun exposed areas. There is no skin, no matter how resilient to sunburn, that will be able to withstand the Florida sun.
This said, let's look at the weather: Although Orlando can be hot any time of the year (yes, even in January!) you can pretty much bet that there will be 90 F temperatures in summer. The summer here is not just June through September. April, May October and November can easily have high 80s climate. Add humidity, which is very common in inland Florida, and it will feel like 100F. In summer most of Florida gets tropical afternoon thunderstorms. They can be pretty intense but usually short. Normal temperatures can be in the 30s and 40 for lows and 60s and up in winter. You will need to bring anywhere from a light t-shirt with shorts to a sweater even in December through February. There is really no way to tell! One day you could be walking around with high 70s to low 80s and a couple of days later see highs of 60F.
The winter can be absolutely beautiful, ranging from morning lows in the 50s to highs in the 80s. Winter is generally low humidity, while summer can see relative humidity in the 70+ percentiles.
Of course there are the hurricanes. Orlando is not like Miami where hurricanes can bring devastating blows every year, but it is still a real possibly. Make sure that if you are visiting, you do not wait for a hurricane to hit. Either make travel arrangements to leave or make sure you can weather the storm with enough food and water. Do not wait until the last moment!
Please purchase an insurance to cover your Disney World trips. I cannot say this enough. Especially with small kids who can get sick often, hurricanes and bad weather in general can happen in Orlando. We had a freak series of tornadoes on Christmas. Orlando was spared but it goes to show that central Florida is very active weather wise at any time!
Beyond the fair warnings, Orlando has a temperate climate all year around. It is not by coincidence that Disney chose this location to create it largest Theme Parks conglomerate.