My family and I have been going to Disney World for the past 15 years in June and it is always pretty hot and the crowds can be overwhelming sometimes. We don't push ourselves to stay in the parks all day so once we know we're tired and need to rest we either find a place to sit down for awhile and just people watch or go back to the hotel room and go swimming. I've found the best thing to do is know when what park has early magic hours and then go to different one instead of that park. For instance, Saturdays we've discovered are good for the Magic Kingdom because I can't remember what park opens early but the crowds aren't as bad and we usually can get most of the rides we want to do out of the way first.