Some time ago, I got a ride in the rear seat of an RV-4. The owner had an aneurysm and explained that there was a very small chance that it would burst and I'd be on my own. The plane had stick and rudder pedals but no throttle. We rigged up a bit of cord with which I could pull the throttle closed. There was no way to increase power by myself.
After the uneventful and quite pleasant flight, I realized that there were some other things we hadn't addressed - no brakes, no canopy latch, no radio. The flight was in the winter and there were snowbanks around the airport. I had visions of driving the plane around the field, unable to get out or even stop, and trying to stuff it into a snowbank, all the time talking on my phone to 911. Yes, this assumed that I could get an unfamiliar plane safely on the ground (I wasn't RV current; I fly a C180) in the first place.
Just mentioning this story so that if you plan to give any control to the back seat, give them enough.
Dave