The driver and passenger are required to be belted in. For all others it's optional. If you ride the Greyhound or Tour busses you're not required to wear a belt. School busses may now have belts but the kids are not required to wear them.
In my coach, it's my responsibility to ensure my family's safety. I allow my grandkids freedom to roam, play games, sleep, watch TV, go to the bathroom etc. while we are underway....it's why we have the coach. In fact, my wife makes us lunch while we are underway, and I eat while driving. Now if, in my opinion, we encounter rough roads, winding roads, heavy traffic or any other reason why I feel they should be seated, my word is taken and they sit. They know the rules and readily comply. Much like the pilot in an aircraft. If the seat belt light comes on, you put it on. It's a rare time though that I've felt they needed to be constrained inside the rig.....Dennis