When children are learning about shapes, especially three-dimensional ones, the easiest way to explain their properties is to give children materials they can manipulate to create them. A simple way to introduce a cylinder is to show kids the central cardboard tube from a used roll of paper towels, as the children will recognise the shape. Then, the kids can make their own examples of a cylinder with just a sheet of paper and some tape.
Face the paper so that the shorter side is closest to you.
Lift up the edge that is close to you with both hands and begin rolling the paper away from you. Keep rolling, letting the paper fold over itself.
Hold the edge of the paper in place with one hand so it says rolled up.
Tape across the edge of paper you are holding so it stays together in a rolled shape: a cylinder.
Have the children compare cylinders, asking why some are thinner than others (because the paper is rolled more tightly). Discuss how even though some are skinnier than others, they are all still cylinders.