> I am not sure how old you are but everything seemed to change when abducted children were put on milk cartons in the mid 1980s. Before that, kids roamed free.
That actually started in the early 1980s, and kids roamed free well into the 1990s.
I don't think there is only 1 reason. I can think of several others - ie Marc Dutroux's case was highly medialised in Europe.
People generally have less and less time with kids due to work, and then overcompensate by being over-protective ("I suck at spending enough time with my kids, but look at how I protect them! I must still be a good parent then!").
There are much more cars everywhere, they drive faster too. Especially US problem from my experience, since whole infrastructure is designed around car usage. How are kids supposed to roam freely in urban areas then? I recall having to do 45 min walk to get to my work which was 1km away in LA, and this was including taking forbidden shortcut via highway road. Otherwise a solid 1h walk, to do frakin' 1km distance. Because nobody thought that there are pedestrians. Well kids are pedestrians, even on bikes.
That actually started in the early 1980s, and kids roamed free well into the 1990s.