Wait till they start getting a paycheck and ask “who is this Fica dude and why does he get so much money from my check?”.
They will not care at all. They're used to lining up like drones at the school nurse's office to get their midday Ritalin dosage and going back to staying in constant electronic contact with their friends. So whether it's Ritalin or money that keeps flowing, and provided they can twitter their friends that they're having a burrito or taking a dump, they'll ask no questions about that Fica dude or any other dude.