I agree with hydro-soil. A kid that age isn't able to discriminate, has no context except what they're taught. If parents aren't aware of this stuff going on they can't counteract it and teach the kids not to believe everything they hear in school, that these people may be telling them bad things and that they should bring home everything so Mommy or Daddy can tell them what's true and what's not, what's good and what's bad.
This is another reason I advocate home schooling.
Get involved... Get quality time with your kid... Get ahead.
Stay Safe!