These creatures come in peace! As party guests arrive, let them launch right into action with a mask-making project. We created ours with glow-in-the-dark craft foam and stickers so we could dim the lights and set an otherworldly mood (you could also use fluorescent materials, then switch on a black light).
Plan an Out-of-This-World Party!

Preparty prep:
Cut out craft foam headpieces with scissors so that they are slightly wider than the mask and approximately twice as tall. Click here to print out a mask template.
Line up the mask at the bottom of the headpiece and trace the eye openings onto the craft foam with a marker. Using the craft knife, cut out the eyeholes.
Use foam tape to attach a headpiece to the front of each mask. (Some brands of foam tape work better than others; if yours isn't sticking well, duct tape works too.)
Draw and cut out alien ears, including a tab on the inside edge as shown so you can tape the ears to the back of the headpieces. Click here to print out the alien ears template.
With a pushpin, poke a hole into each Ping-Pong ball.
During the party: The kids can make antennae by inserting a pipe cleaner into the hole in each Ping-Pong ball, then attaching the other end of the pipe cleaner to the back of a headpiece with duct tape. They can use the foam tape to attach alien ears and googly eyes, then decorate the masks with stickers.