There was a thread about this a while ago, I will see if I can find it.
When we went last April, we were standing in line for Dumbo when Goofy and Donald boarded the ride. First, they rode alone, then the CM at the line asked two kids if they wanted to ride with them. I think she just took the first two little kids she saw. I'm pretty sure that she was going to ask DD, but there was a developmently disabled boy next to us (probably 18-19 years old or so) and his mom figured out what the CM was doing and said, "he would love to ride with Donald." It was fine with me, because I don't think DD would have done it anway. But, we were on the ride at the same time as the characters.
Then, Donald and Goofy got off the ride and quickly walked away. We managed to snag a pic with Goofy before he escaped.