This activity helps children develop a sense of sizing.
There are two ways to play.
1. Get several jars/vases and trace them on paper. Talk with your child about what could fit in the jar. Have him or her get the items and see if they will fit within the boundaries of what you traced.
2. Get different sized jars, tupperware, etc., and let your child actually try to put stuff in there. Beware--if you child is attached to something that goes in but not out, you might end up breaking a jar :) My suggestion, do this only with wide-mouthed containers (like old Peanut butter jars) or plastic items you don't mind cutting (like a milk jug).