Get the
Disneyland Sing Along Video (sometimes it's called "Disneyland, It's a Small World").
Anyway, it's circa 1989-90 and only available on VHS, but it has the "live" characters (as opposed to cartoon drawings) singing songs all over Magic Kingdom.
We did this as well. Worked Great. Except on one of the videos we always had to fast foreward through any villians. We knew to stay away from those on the trip.
Also, we made the mistake of going on the Pirates of Carribean. (We had forgotten what is was like) Our 3 year old was terrified. We rushed him on to Dumbo as soon as we were done. It erased any bad memories. (He is now 9 and doesn't remember the bad experience)
Good Luck!