We do the single rider line a lot at RSR at DL and TT at WDW. The only issue with TT is that you don't get the full car design experience. You still get to go by the kiosk and "design" a car, but really it is just giving you a selection of a few pre-done cars instead of the full design experience and options. With the FP+ tiering, and the long lines, it is often worth it just to do Single Rider. The wait time will be posted for single rider. If you keep an eye on it, you can usually find it within the 10 to 20 minute range at some point during the day. DD has done it since she was 7. I was a little nervous the first couple of times, but she was not as she is a pretty independent outgoing kid. DH and I will put her between us, so one of us is in front and one behind her, in hopes that one of us is off the ride waiting for her or with her, but you must realize that the way they pull people- a kid can wind up in a car in front of you or in a different ride cycle. She loves it if she is pulled for a spot with a kid next to her- so if the front one of us is getting pulled for row with a kid or we see the rear one is going to be, then we switch. She has strong instructions that she is to go to the area where they display the ride photos and wait there for us. She is also instructed that the ride could break down or get stuck while someone is on it and if she is already off, and it is taking a while before she sees one of us, that is what likely happened and to stay put--- and if she is on the ride and it is stuck, know that if we are ahead of her that we will likewise stay put. In other words- the photo area is the spot and no one is to move until everyone is together again! More often than not, one of us is in the same ride cycle with her and getting off at the same time, but I do remember one time that she was in the cycle ahead of us.