All The StarsPut a picture of each child on a star with the heading "Welcome To All My Stars"
Alternatively you can write your children's name on their star.
My Own SpaceshipGo to a convenient store and ask if you can have (or buy) the lids for Icee cups (most stores are happy to donate them) next let your children help you paint a space theme on paper to put on the bulletin board (complete with stars, planets, moons, etc.) Put your children's pictures under the Icee lids all around the board (looks like their in space ships). Finally, ask your children if they were an astronaut where would they go? And write their answer under their spaceship.
Starry SkyGive your children cardboard stars and aluminum foil. Let them cover the stars with the aluminum foil and then decorate the star. Next let your children create planets, a sun, and rockets. You can use titles like "Reach for the Stars," "Upward Bound," etc.
Birthday StarCreate a star for each child's birthday. Make a big star in the center of the board. During the month of the child's birthday put their star in the center of the board. Children that do not have a birthday that month surround the big star. Title the board something like "This Months Stars," "A Star Was Born On," etc.