You have to make it personal. One of the ways that this might be explained--the tradition of the poppy--is that in the soil of Flanders, when bodies became buried in the middle of the battles, when shells would blow earth up into the air, people could tell where a body was because poppies would come up. The decomposing flesh worked with the soil and the chalk in that area. This is why the soldiers adopted it.
When you point that out to teenagers in those terms, they make the connection between a poppy and what it really means.
Remembrance has to be personal. What can we do for our veterans? We can listen. Just be there. Show up at an event, buy a veteran a Pepsi, and just stand there.