Cylinder StackersGeometry in action: A cylinder rolls and stacks. A right cylinder's base is perpendicular to it's curved surface height. The two base circles are parallel to each other. Go for a cylinder hunt with your kids...poke around junk drawers, your pantry and through your closets to find all kinds of example of cylinders or cylindrical objects...bottle tops, pencils, cups, oat cans...
Gather a bunch of paper towel or toilet paper rolls. You may wish to spray paint the exteriors and let them dry. Let your child paint the cylindrical rolls with tempura to make the stackers "their own". Cut the rolls in half, in fourths or thirds when they dry.
Cut two slits on the top and bottom of the rolls. The slits can be about a half inch apart or so. Slide another tube stacker into those slits. Your child can create a structure of cylindrical tubes by sliding tubes into the top and bottom slits of each stacker.
You may wish to play with the stackers and create a structure with unpainted tubes. Then spraypaint the whole structure and let your child paint the whole thing with tempura. The tubes will be sort of glued by the paint, so this may be more of a one-time use of the tubes. If you paint the tubes first and let them dry before you stack them, you can reuse them.