We had a 9 yr old with us a few weeks ago. We let it be up to him 'Do you want to ride Everest twice but we have to go single riders, or do you want to wait in line and we only get to ride it once but we go together?' (It was true, that was our first of four planned hops that day.) He said he wanted to ride it twice. First time, he actually did get to ride with one of us (that's when these giant tour groups come and they don't want to split up a group of 8 so they pull two from the SR line to fill up the last car and the next train can accommodate the big group. Doesn't always happen but great when it does.)
So our plan was to make sure one of us rode down first so we would already be waiting for him at the exit. The second time, he did have to ride SR and he had no problem with it. His grandma thought he would be terrified but he wasnt. He was smart, ride it twice as much for half the line. She later took him on SR for RnRc too (our FPs were at MK, which was the 4th and final hop.) He got to ride his faves a bunch due to SR and it worked out just fine. We did keep an eye on him and made sure he got loaded on to the train. After that, we knew we would be there first at the exit so it was fine. He's riding like a big boy pro now!!! (Last yr was the first time he was ever tall enough for Rc) I don't think it would be a problem if the SR adult didn't ride, took the chicken exit, but its never ever occurred to us...