An activity my 3 year old has enjoyed since he turned 2 is playing with cornflour/water. Sounds random, but when these two are mixed some random chemical reaction happens and it appears solid but try shaping or picking it up, it turns to a liquid. It can get a bit messy but my boy can play up to a hour with it, and now he’s learning about solids/liquid! You can give them a straw/spoon or even colour the corn flour to make the activity abit different.
To make this slime mixture; simply add x many cups of cornflour and exactly half the amount of water – i.e.: 2 cups cornflour = 1 cup of water. The mixture should be thick enough for you to pick it up and when you do it should turn to liquid.
Enjoy endless fun!