We had a science party for my son's 6th birthday.  For invitations, I got blank cards and cut a beaker shape in the front of the card. I got some see-through, sparkly paper and attached it to the inside of the card so it looked like the contents of beaker.  I wrote "Mix it up at Bob's 6th Birthday" on the front and put the party details inside. We did most of the experiments at the same table which was covered with a couple of plastic table cloths.  When things got messy, we removed a table cloth and had a clean surface. My husband wore a lab coat, hair net, safety goggles, and shoe covers - several of the kids asked if he was a "real scientist".  The experiments were: 1)ICE BALLS  Fill and freeze a water balloon for each child.  Put the resulting ice ball in a tray and give each child a salt shaker, dropper, and dish of colored water. I got cheap salt shakers at the dollar store. The kids sprinkled salt and added colored water to their ice balls for almost 1/2 hour. When we were finished, we put the ice balls outside to see what happened when they were left in the sun. 2)LAVA LAMPS  We pre-filled each 12 oz. plastic bottle with 4 oz of water and 8 oz of vegetable oil. The kids added color (food-coloring) and pieces of alka seltzer which fizzes up and makes great colored bubbles.  When they were done, we put their name on the bottle and sent it home. 3)We took a break to open presents while we cleaned up after the lava lamps. 4) SNOW.  I bought instant snow from stevespangler.com. We put out trays with a cup of snow mix and a cup of water  When the kids add the water to the snow it expands A LOT!  Each child got to make two cups of snow which we sent home in a plastic bag.  The snow eventually dries out and can be re-used. 5) Eat Cake. 6) SODA FOUNTAIN.  We did this in our driveway.  Add a package of Mentos candy to a 2 liter bottle of soda and it shoots most of the soda out of the bottle. The kids were really excited.  We did this a few times, but didn't have each child do this.  (Although, they really would have liked to do it.)  Then, we went back inside to pack up and hand out party favors. Party favors: Bags of instat snow, lava lamps, a science folder I bought for .15 cents each with a list of the experiments we did including directions and ingredients, and plastic test tubes filled with candy.  The test tubes had been sitting in test tube racks on our table as part of the party decorations. The whole party took about 2 hours.  The kids had a great time.  I wish I had covered the floor around the experiment area.  It would have made clean up much easier.  But, overall, it wasn't too messy.  We got a lot of ideas from www.stevespangler.com.  This website includes videos of experiments and you can buy a lot supplies there too.  The web site also tells you how to do a lot of experiments with materials you have at home so you don't have to buy a lot of stuff.