S.D.
You could do a space theme. Get glow in the dark stars and lanterns and do things outside in the dark. Play hide and seek in the dark. Kids can just stand anywhere.... can't see them. Have the seeker play in pairs. You could have them make the planets out of playdough, you could do sidewalk chalk the glows in the dark and have a contest for the best planet drawn. You could make rocket ship cake and / or cookies.