One accessory you might consider bringing with a 3 year-old: EARPLUGS!
I know the saying "If it's too loud, you're too old." Well, probably so, but WOW is everything loud! Somebody decided that an attraction can't be good without concert-decibel volume. DS (4 at the time) spent four days at WDW with foam earplugs in 75% of the time. Even Muppets and Playhouse Disney were loud!
They are small, don't take up much space and can be a real life (and hearing!) saver. Check your local Mart in the health and beauty aids section for the foam ones.
Really, I'm not a freak about hearing loss. I was just surprised at how loud everything was.
Just my two cents. . .
D-n-C