Make an erupting volcano. Materials: foil cake trays or other trays to catch the mess. Fast Mache, Plaster of Paris, or some other fast acting molding material, vinegar, baking soda, water, food coloring, plastic spoons, small paper cups. Liquid soap is optional for more interesting eruptions. Also optional is fast drying model paint to make the volcano look more real.
Place container on tray and mold the volcano around it. Don't worry if the volcano looks lumpy and bumpy. While waiting for your volcano to harden you can put left over plaster in a plastic baggie and shape it into something else - dinosauers, animals, people, etc. Mix a spoonful of water with a spoonful of baking soda and place it in the container. Then add a drop of food coloring (and liquid soap if desired) followed by a spoonful or two of vinegar. Watch your volcano erupt. Stirring it and adding a little more vinegar will make it erupt more.
For snacks, have a bucket of dirt made with chocolate pudding to which is added gummi worms and broken up graham crackers.
Grow a pet TickleMe Plant from seeds and watch how the leaves fold and the branches droop when you Tickle it! They are easy to grow in the TickleMe Plant party favor and it's a fun way to learn about plants.