This was my 5 year olds favorite thing as a toddler. I would make kilos of the stuff at a time because he went through it so quickly. He would play with it mostly outdoors and my backyard often looked like it had been raining hundreds and thousands!
This is a great sensory activity using hands (or scoops, spoons etc) but also a great sorting game. Leave the colours unmixed and use different coloured cups to sort the rice into.
This will keep for 12+ months in an airtight container. Discard if it becomes wet.
I have given the instructions for the thermo mixer however it’s just as easy to use ziplock bags and old fashioned muscles.