Watching the earth's shadow slowly swallow up the moon and spit it out again brings expressions of amazement and awe from your little one. His reaction is worth letting him stay up late so he can watch and try to puzzle out why the eclipse happens. You can use various activities to explain the phenomenon at his level.
Preschoolers are curious about why and how the eclipse happens. Give your little one a large yellow circle for the sun, a circle that looks like the earth, a circle that looks like the moon, and a cone-shaped piece of blue cellophane wrap to represent the shadow. Glue the sun to the left side of a sheet of paper, but leave the earth and moon models free. Adjust the moon and earth to display various ways a lunar and a solar eclipse can happen, using the cone to represent how the shadow falls in partial and full eclipses. Alternatively, have your children hold each paper model or balls and let them create models they can understand.
Create Your Own
Use a lamp and plastic or polystyrene balls to create your own eclipse. Your preschooler will enjoy holding one of the balls in the model. By shifting the position of the earth and the moon, you can demonstrate a lunar and solar eclipse in various stages and forms. You could put together a diorama using clay balls and strings to create an eclipse model, or hang multiple polystyrene balls from the ceiling of your child's room to create several eclipse types, using the overhead light for the sun so he can study the many ways eclipses happen.
Young children love stories, and you can read to your little one about eclipses. Consider books such as "Sun and Moon" by Marcus Pfister, "Sunpainters: Eclipse of the Navajo Sun" by Baje Whitethorne, and "Sun and Moon: A Giant Love Story" by Lisa Desimini. Your child can act out or retell the story with puppets after you finish reading the book. She can also make up her own stories about how the shadow eats up the sun or the moon. She might understand why ancient cultures were afraid of eclipses and explain how she would feel if she thought the moon or sun would never come back.
If there will be an eclipse in your area, take your child to an eclipse watching party at a local planetarium or museum of science. Some of those parties provide telescopes your child can look through to see the eclipse. Alternatively, check out video replays of the eclipse at a children's museum or on the Internet. The video displays of a solar eclipse might be safer and less scary for your young child than actually viewing the eclipse in person.