It will be very hot and humid there (of course you are from TX whereas I am from MN so perhaps you won't mind as much). We did a Disneyland vacation in the middle of summer once and to beat the heat, we would go first thing in the AM to the park for maybe 3 hours, then go back to our hotel for lunch and the kids would play in the pool got awhile, then go back to the park late afternoon/early evening when it cooled off again and people started to leave. Of course, that was with my 10 year old step daughter and her cousin, so maybe they could handle being up a bit later than your kids.
I just say to be cautious of being at the parks all afternoon in the sweltering heat and your kids standing in endless lines getting ornery.
I'd also say to take a couple days and just hangout by the hotel pool or drive to Cocoa Beach, kids seem to love water more than anything else.
Also, make sure you check out FastPass or whatever it is called that allows you to skip the longer lines for some attractions.