Lenore at Free Range Kids has a link to an article at a "mommy site", that boils down to: Men who speak to children are paedophiles. No really, I'm not making this up.
Personally, I try to avoid reading parenting sites as they make me want to reach up, and yank out my uterus, with both hands. If they aren't promoting the latest terror awaiting your children, they're setting up the cyber pillory for women who balk at being reduced to the roles of incubators and protection units. God help you if you fed the kid formula, or had an elective c-section. Depending where you live, your foetus has more rights than you do. And now you're going to let them talk to strangers? Male strangers? If this were a mommy blog I'd have to follow that with sixteen exclamation marks.
So remember, if an unfamiliar old man starts asking your kid about multiplication tables, he's probably grooming him for sexual favours, or a degree in advanced maths. Be prepared to scream should he produce a slide rule.