bowl with water
random assortment of materials some that sink some that float
I taped off our tray into sections so once they figured out whether something sunk or float they could put it in one square or the other.
This is a fun game the kids love playing in water and they love discovering which items sink and which float. Its fun to if you want to let them go around and collect more items to discover if they sink or float. I also like having the kids make a hypothesis before they drop each item in to the water trying to guess if the item in question will sink or float.