To make the volcano itself we took the side of a large cardboard box as a base. In the middle of this we stuck an upside down yogurt pot and then another pot on top (this will hold our bicarbonate of soda etc later).
At this point cue the scrunched up newspaper and masking tape to build it up into a volcano shape around the pots.
Next comes the boring messy bit. Layers of newspaper and glue. Although there are recipes for making your own flour and paper glue (just use Google you will get hundreds) I prefer to use a watered down PVA glue. You can buy two litre containers from building merchants where it is sold for sealing bare plaster walls before decorating - the last container I bought was when A was born and he is now 7! To use add roughly equal amounts of water and glue so that it looks like milk. This saves a whole lot of faffing about boiling/mixing/cooling and if you need to spend several days making your model (and lets face it it is not the most interesting thing in the world to do all day) it doesn't start to stink!
Once all the paper was dry R painted the model.
To make the bubbling larva. Put some bicarbonate of soda (also known as baking soda and has the formula NaHCO3) into the yogurt pot. Carefully pour in vinegar (with a little washing up liquid) that has been tinted with red/orange food colouring. You should get a bubbly mixture that goes down the side of the volcano. Of course since R wanted to do this at school we had a trial run first before she had to do it in front of her classmates with an identical sized pot to see how it would go. Just a note don't use baking powder for this experiment -although it contains bicarbonate of soda as an active ingredient it doesn't work so well as the pure thing.
For those interested in the chemistry part vinegar and bicarbonate of soda is an acid:base reaction. The bubbles of gas are carbon dioxide.