A runner can advance at their own risk in the event of an infield fly. I would think that a lot of younger players do not understand this rule and when they see the ball hit the ground, they immediately take off for the next base. It is important for coaches at a young level to teach their players this rule.
I bet that most major league players would fail a test about the nuances of the Infield Fly rule. In fact, I wonder how many major league players who were on base during an infield fly and then saw the ball dropped by the fielder would take off running to the next base?