Popsicle Stick Orbit
Have your children decorate a washer as a planet and a popsicle stick as the
sun. Attach the washer to one side of a piece of yarn and the popsicle stick
to the other (helps to cut a notch in the stick). Tell your children to hold
the sun (Popsicle stick) and spin the yarn causing the planet to orbit.
Lite Brite Constellations
If you have a Lite Brite use it to make constellations, your children will be
able to see the constellations much better on a Lite Brite.
Rocket Launch
Place an Alka-Seltzer Tablet and a little water in a 35mm film cartridge and close
the lid tightly. Place this on the floor and stand back. The top will very soon
launch (the pressure from the gas causes the lid to pop off and fly about chest
high) 
Telescope
Put two pieces of black tissue paper at the end of a paper towel tube and fasten
it with a rubber band. Using a small object (pencil, pen, paperclip, etc.) punch
several small holes in the tissue paper. Next let your children decorate their
telescope however they see fit. When your children look through the telescope
and hold it up to a light they will see stars!
Coffee Can Galaxy
Put black paper around the inside of a large coffee can, then put three marbles
(or one ping pong ball in a mixture of white paint and glue. Next take the marbles
out and spoon them into the coffee can. Have one of your children shake and
roll the can. Finally take the paper out and let your student put stars on the
orbit path created by the marbles.