You can make a model of a erupting volcano. For making it make an model of a volcano with mud or cement on a base, then after drying ,colour it for getting it a look of a volcano. Than take some food color(red) and mix it with vinegar until it formd dark red vinegar. Than pour the mixure into model of volcano. Than during the show time just add the baking soda in the proportion of 2:3 in to the model containing vinegar. You can see the lava coming out of the volcano
In this model ,inside is the reaction of baking soda and vinegar causing it to come out like a lava. for making it to look like a real lava we add some food coloring .