This morning my oldest son (who is about 5-1/2) asked me, "Mom, what's a stranger?" This question probably came up because the doorbell rang yesterday and he answered it before Daddy or I could get there. (It turned out to be our next-door neighbor, Miss Audrey, bearing Christmas treats — definitely not a stranger.)
Since we haven't really talked a lot about "stranger danger" I took the opportunity to explain that a stranger is someone you don't know... and that the problem with strangers is that you don't know if they're kind/good people or bad people with bad intentions.
Anyway, we talked about what could happen... that if a stranger were "bad" they could take him from us and hurt him, and then how would we find him? (I was hoping that this would impress upon him the need to use caution around people he didn't know.) Then he asked, "Would they steal our toys?" I said, "Possibly, or our computer, or our money. Or even our car." And he replied, "How would they steal our car? It would be too big to carry!"