P(adult evil | talk to them) < .0001
P(stranger evil | they talk to you) > .0001
[1] http://www.pollyklaas.org/about/national-child-kidnapping.ht... [2] http://www.childstats.gov/americaschildren/tables/pop1.asp
Just to share anecdotes, I had a few memorable experiences as a kid (and probably many more that I don't remember).
A very nice person helped fix my bike chain when it slipped off the gears and got wedged against the frame. Without them, I'd have a long walk home with a stuck back wheel.
On another occasion, while I was playing outside my house, a man came by and invited me to attend his church. My parents weren't keen on that, and I was rather uninterested so we never took him up on the offer. I presume he was a Jehova's Witness or a Mormon.