When I lived in California,
Disneyland had a single rider line for Toy Story Mania. I used it all the time. I went back to find they got rid of it. I asked why and was told parents weren't happy that their kids could be seated with an adult stranger.
As an adult gay man, I am VERY concerned when a child is seated with me. I know that *I* would never do anything, but I know that people are lawsuit happy and it would be very easy to "claim" a false charge.
To me, if the ride has seperated seats then I am more comfortable with being seated with strangers. If there is a bench seat, then I would definitely refuse to be seated with a child.