Have the kids measure the value of Pi.

Have them draw as big a circle as possible.  Measure the circumference.  Measure the diameter.  Divide circumference by diameter.  Quotient ought to come out 3.14159.  Small errors are probably due to crude measurement methods.  Large errors are some kind of blunder.  Repeat the exercise on other circles just to make it clear that Pi is the same for all circles.  This will give some practice using the calculator and give a real feeling for the size of Pi and what it means.  To draw big circles you can use a pencil stuck on the end of a yardstick and pivot the yardstick off a nail.  Or tie the pencil to a string.