To show the children a chemical reaction I got out the bicarbonate of soda (baking soda) and vinegar. I put a bit of bicarb in the messy play trays and then filled some plastic egg cups with malt vinegar. The children added the vinegar to the bicarb and loved the fizzing sound and watching the bubbles and flow of the mixture. I explained how the bubbles were carbon dioxide which is the same chemical we breathe out. Here's the scientific explanation
Food colouring could be added to the vinegar in the egg cups for dramatic effect and to show what happens when different colours are mixed.