In fact they can even be more deadlier. I know, top of the mind, of at least three very very tragic accidents, where the drivers of the cars escaped with minor injuries whilst those in the back seats died!
Belting up will help of course..and yes it should be made mandatory for grown ups as well to wear seat belts regardless of where they are seated in the car. Many people focus so much on getting the kids to wear their belts, yet can be very careless about themselves.