P.N.
It's not that bad. Swim a lot, take frozen water bottles into the parks with you. CUPS (not bottles) of ice water are FREE for the asking at all park quick service counters! Time breaks from the parks to be in the hot part of the afternoons. Little water bottle fans are great for the kids, and Walmart usually starts carrying those about now for like $5 apiece. Spend time in the air-conditioned parts of the hotels and resorts at those times. We would often take a Disney bus to one of the super fancy resorts (Grand Floridian), in the afternoon and explore inside and outside the resort to help beat boredom and heat.
Have fun!