Are you asking about things that weren't considered dangerous when I was a kid, but are now? I always thought that was largely a cliche? Pretty much everything that I did as a child that is, or could be, considered dangerous today was considered dangerous then, too.

One thing that does come to mind: I don't think the general public back then was as aware of the danger of second hand smoke. So, exposing kids to cigarette smoke (by smoking indoors, in cars, or even going to public places with smoking sections) didn't seem to be considered risky or dangerous.

Otherwise, pretty much everything I did as a kid that would be considered dangerous today would also have been considered dangerous back then in the days when dinosaurs ruled the Earth and the wheel had only recently been invented. That includes activities sanctioned by adults, like riding in the bed of a pickup truck, and those which weren't, like mixing random chemicals together to see what happens.