Build an actual, working battery, using simple materials commonly found at home.
A very easy experiment to create hard shapes simply by curdling milk with ethanoic acid.
Experiment with the science of density by stacking different liquids in order to make a colourful tower.
Store in a balloon the light (Hydrogen) gas produced from a chemical reaction. This gas will combust in the presence of oxygen, causing a small explosion to occur.
A simple activity illustrating the breaking down of colours by bleach by turning coloured solutions into colourless ones.