There is a thing going round on facebook, its fairly old, but it looks like fun for something to do with a toddler.
So you get a saucer of milk and add food colouring in, then add dish soap (or fairly liquid in my case)
I may have mentioned that I do have a creative bone in my body, and not even a scientific experiment which triggers a chain reaction, that involves a creative twist would work for me.
So we watched it on you tube instead