How will you tell an 8yr old kid what oxidation is?

Go to the driveway: I love stuff like this! show your little beating heart your shiny red corvette and have him see it and feel it saying, "now, that's normal red paint!" go over to your neighbor's house and have him look at the old beat-up 1967 vw bug with rough, salmon-colored, paint, and say, "this is oxydized red paint!" the oxygen molecule adds to the normal paint and changes it. This happens with everything.