Also - teenage mortality has reduced drastically[1]. It's hard to argue that could be a bad thing.
It is probably because we don't let them (wherever possible) carry out activities that might kill themselves.
I am a parent of 3; I will happily take my children mountain climbing, skiing, snowboarding, trekking, wild swimming. In a few years we plan to trek to Everest Base Camp and they are coming with me to the Andes.
We engage in controlled risk. If they break a limb skiing then they break a limb skiing. They pushed beyond their abilities in some way. I don't need to give them wrappers of cocaine from a criminal and a handgun to be a better parent.
There is also a very real risk of the "Tom Sawyer" bias. Each generation thinks their generation took greater risks and had more vivid adventures than the one previous. The cognitive dissonance curiously avoids the higher levels of child abuse, abduction, injury, poisoning, asphyxiation, malnutrition and disease. My father used to have great adventures playing as a child in asbestos riddled houses. You can talk to his friends about it sometimes...well the few that have not died before 60.
Oh look here is a group of kids that used lethal asbestos as chalk. [2] They really learned a valuable lesson about ad-hoc citizenry there.
[1]http://www.cbs.nl/en-GB/menu/themas/gezondheid-welzijn/publi... [2]http://www.bbc.co.uk/news/uk-england-tyne-24942338