Tara is taking a liking to anything science and always asking to make the dinosaur volcano's that we made some time ago. http://homelearningfrombirth.blogspot.com.au/2011/04/volcano-dino-land.html
The following activity is a little less messy and great for a rainy day.
Pour a layer of bi-carb soda onto a tray. Fill up a glass or (a few if you want more variety) of vinegar and drop in your favourite food colouring. Use a dropper to transfer the coloured vinegar onto the bi-carb tray and watch the science take place!