When the aliens attacked they would leave stars and moon shapes on objects. They left those marks on the kid's playhouse. Later in the movie though they disappear. Where did the stars go?
They're still there. In fact, when Merrill comes up out of the basement after the aliens leave, when he reaches the top of the stairs, you can see the moons and stars all over the wall, like they're casting reflections. Funny you should mention this, I always just thought it was a pattern of the outside shed, like the owners are really in to celestial things, you know?