Decorate: Buy silver paper goods. Hang planet-and-star mobiles (use Chinese lanterns for planets and cutout poster-board stars).
Eat: Serve astronaut ice cream (freeze-dried; find at sports stores) and "rocket dogs" (hot dogs in foil).
Make: Rockets from toilet paper or paper-towel rolls, cone-shaped cups, foil, and stickers.
Play: Space flight! Create a solar system on the floor with concentric rings made of tape or string. Tape construction-paper planets in place, with the sun in the center. Have child stand on the sun, blindfolded. Spin him, and let him toss his rocket. Where does it land?