If you go with the PB&J example (and you should!) You should make up little blank signs to be your "Variable Names"

That way you can label the knife "Knife" the bread "Bread" (here's where it'll start causing errors) Name the slices of bread "Slice_1" and "Slice_2" so that when the kids shout out "Put peanut butter on the bread!" you can smear peanut butter on the bag of bread. :-)