A student read about Volkswagen-packing in the 1960s. She asked about the maximum number of students that might have fit into a Volkswagen. How would you help her estimate an answer in a reasonable way?

Google <Volkswagen packing record>

You will find this reference:
http://www.thefreelibrary.com/Bank+of+America+Sets+World+Record%3B+19+Bankers+Stuffed+Into+'98+VW...-a050140780

In 1998, the record was set at 19. The "stuffees" were adult bankers, not children.

You could make an estimate by dividing the interior volume by the volume of an average (but not obese) person. But that would take time.