personally i always have
there are a few under 18's that i have worked with quite often and i have always picked them up from their homes, got out and spoken to their parents etc before setting off, but for the first time shooting with them, i called in and had a chat with them
it gives them a change to size me up and ask any question that they may have. also left them with a business card with all my contact info on it, folio address, bebo address etc etc, so they know where to contact me at any point
i was always working on location, and the parents were never to keen on going and standing about during a shoot, so i found meeting them before hand always made them feel that bit more comfortable with it, and over time i have ained their trust
If it had of been studio shoots i would of insisted on a parent being there