The route was quite wheelable (we saw quite a number of other visitors using mobility equipment), and there were accessible buses from the park-and-ride sites. And the second float we saw was.... the Lions Club International float, titled "the Miracle Worker," with a giant black-and-white image of Helen Keller and Annie Sullivan (made of rice, poppy seeds, and onion seeds, we were told); behind it, a giant pair of glasses, a white cane, and a stack of books titled "Braille," "Helen Keller," "The Miracle Worker" etc. The "white suit" at that float showed us a braille version of the Parade program, and invited the kids to feel the braille pages.
Further along, another "white suit" invited us to go inside the barriers to touch a float and examine it at even closer range. Apparently this is an accommodation offered to disabled visitors--so my son was soon holding a starfish made of lima beans and whiffing irises.
[Photos depict the Lions Club float as described in the text of this post.]