Items to discuss:

Have five students come to the front of the classroom and hand each of them one ball. Have them face the class holding their ball.

Talk about how the stars are different sizes.

Have the students put themselves in order from the largest to the smallest.

Discuss how the Sun seems big because it is so close. Really compared to some of the other stars that are bigger, the sun is small. The other stars appear small because they are so far away.

Discuss that the balls are different colors just like the stars.

If you want to show an ACTUAL size comparison:

Use a huge paper Betelgeuse that hangs on the wall or from the ceiling. The actual size will need to be about twelve and a half feet in diameter.

Use a paper blue Rigel 35 inches in diameter.

Use an orange paper Arcturus 14 inches diameter.

Tell the students that we use the paper because there is not a ball that big.

The student holding the yellow Sun walks over to the red paper Betelgeuse and we see how big Betelgeuse is compared to the sun.

Then compare the sun to the paper Rigel and the paper Arcturus.