When we purchased our Class C in 2009, our kids were 6 and 7 (soon to be 8) and both no longer need car seats in the state of GA, so for us it wasn't an issue. My sister-in-law and family has traveled with car seats in their Class C without a problem. There are special car seats that are made to be used on the sofa, sorry I can't remember the brands or models.
To answer your main question - our kids were always belted when they were in the motorhome while traveling unless they had to go to the bathroom. If they needed anything, my wife would get it for them. When they were teenagers we gave them a little more freedom, but they were still required to wear seat belts at all time. Our motorhome had 6 seat belts (not including front seats) - 2 on the sofa and 4 on the dinette.
Before the motorhome, we owned a Hybrid TT. Even though both of our tow vehicles were comfy on long drives, the motorhome was a much nicer way to travel.
-Michael