It is annoying for sure. I don't often pay much attention to what age said kids jumping around in a car are, but usually you can just tell they need to be in a seat.
Ad far as our parents ect...sure cars may be safer these days, but they are faster, there are a heck of a lot more of them too.
I know busses are tanks, but I am surprised they don't have belts yet. Just hard to account for all the OTHER cars on the road.