Hi Donna,
Since you will be heading to the parks before many schools have begun their summer breaks, you should have lighter crowds (yea!). The average temperature in May is 77 degrees, so it should be quite pleasant. In fact, you are visiting during one of my favorite times because of all those reasons.
As for things to do, I'd make sure to visit the
Epcot International Flower & Garden Festival, which takes an already beautiful Epcot and transforms it even more so. While I don't know the dates for 2013 yet, you may find Disney's Hollywood Studios adventurous with
Star Wars Weekend, which is scheduled for the spring of 2013.
Similarly, you'll be able to enjoy the
new Fantasyland at the Magic Kingdom that just opened, and I'd certainly try to make reservations for
Be Our Guest. Also,
Test Track at Epcot has re-opened with new theming and experiences. If all of that isn't enough, Downtown Disney is celebration the addition of
Splitsville Luxury Lanes, which is a 2-story, 50,000 square foot bowling and dining complex.
And of course, there are 4 amazing theme parks, shopping at Downtown Disney, and 2 water parks if you find yourself bored with all these spring experiences! If we can help with anymore questions, please let us know. Wishing you a magical trip!