It looks something like this:

-explain oxidation / combustion

-explain what’s needed for combustion

-light a nail (fail)

-light a candle
+what’s happening?
+cover, remove oxygen–>stop combustion by removing an essential part

-why can’t you light metal?

-light a magnesium strip w/clip (let it burn out)

-re-explain what is combustion? why does magnesium combust?

-kids hypothesize: can magnesium burn w/o oxygen?

-explain why you need to polish the magnesium

-light magnesium, cover

-kids write conclusion

epilogue: light a bunch of magnesium and drop it in hot water (IMPORTANT: near open window)