I moved this from the disABILITIES Community Board to the disABILITIES Board.
The handicapped viewing areas are marked on the park map for each park. You should check the maps when you get there because they sometimes change the location slightly (often across the street or down a little from where it had been).
Many of the areas are not that large and often fill up quickly, so plan to go to the area an hour or more before the parade/show.
These are the current locations as of May 2013.
Magic Kingdom has day and evening parades and the handicapped viewing areas are the same for both. The areas are in the hub in front of the train station, in the castle end of the hub and in Liberty Square across the street from the Hall of a Presidents.
The fireworks show is centered at the castle. There is no handicapped viewing area for it.
Animal Kingdom has only a daytime parade. The handicapped viewing areas are in Asia in front of Flights of Wonder, Discovery Island near the entrance to Bug's Life and Discovery Island across from Pizzafari. There are no evening parades or fireworks.
Disney Hollywood Studios has a daytime parade. The viewing areas are on Hollywood Avenue in front of Min and Bill's Dockside Diner and in front of ABC Sound Studio.
There are no fireworks, but there is an evening show called Fantasmic. This is performed in a large amphitheater near Tower of Terror. There is handicapped seating in the back 3 rows of seating (the very back row is wheelchair spaces and the 2 rows in front of that are for guests who are not using a wheelchair plus the rest of the party).
Epcot has no daytime parade. The fireworks are a music, light, laser and fireworks show in the middle of the World Showcase lagoon. There are good viewing spots in many areas and if you arrive early, you will be along the fence with no one in front of you.
The handicapped viewing areas are in Showcase Plaza along the water near each of the shops (2 areas), in front of Germany and between the United Kingdom and Canada.