Joe and Jeff,
Jane Shaw and I recommend this classroom exercise in our book Facts Not Fear. Give two thirsty kids one glass of a soft drink and two straws and watch what happens. Ask the class what happened and why?
Then give two more thirsty kids separate half-filled glasses and two straws. The first example illustrates the “tragedy of the commons” and the second private property rights.
We found one teacher who solved the “Lego” type problem by establishing property rights for each toy in the classroom and then kids could decide if they wanted to share or not.