Use fun experiments to teach the scientific method instead of trying to impart on them a superficial understanding of chemistry and geology (in the case of the volcano).
For math, try to address any form of mathematical anxiety. I think that is more important than whatever knowledge you could teach them, but if you can make it engaging I recommend introducing some logic and naive set theory. Combinatorial problems are also easily illustrated with physical objects and can serve as an introduction to probability theory.
Use fun experiments to teach the scientific method instead of trying to impart on them a superficial understanding of chemistry and geology (in the case of the volcano).
For math, try to address any form of mathematical anxiety. I think that is more important than whatever knowledge you could teach them, but if you can make it engaging I recommend introducing some logic and naive set theory. Combinatorial problems are also easily illustrated with physical objects and can serve as an introduction to probability theory.