I would suggest lots of visuals and demonstrations. Pouring a teaspoon of oil over a pan of water?  Problem is that would ruin your pan. Something like that. I would say the more encouraging and empowering you can be the better.  People this age are really looking for empowerment and independence. There is a great National Geographic short on a water pump in Africa run by a merry go round.  I would be really impressed if you can get the kids thinking of the oil under our earth as theirs.  Like Air and water, it belongs to them and they have a right to it. Imagine if petroleum was rationed, like it was during world war two, and every kid in your class had a coupon for a barrel of oil.  They could sell it, save it, use it to run a car for a short bit, or use it to make medical grade plastics and saves lives.   With 6+  billion  people on the earth, what is each persons fair share  of the remaining  crude?  Peace, Art