A tall,thin jar or container (the height of this will determine the height of your volcano)
Red food coloring
Make sure you have enough to Play Dough to form a volcano around your jar or container.
Roll the Play Dough into balls, divided evenly so that there is one ball for every guest at the party.
Pour some vinegar into a separate container (not the one you're using in the volcano!) and add in a few drops of red food coloring until it looks like "lava".
At the Party:
Explain to the children that volcanic eruptions help to form new land. As Molten lava from the Earth's center spews out onto the ground, it cools and becomes new land. Also, some scientists believe that the dinosaurs may have been killed off by tremendous volcanic eruptions which covered the Earth.
Center the tall, empty container on the cookie sheet.
Give each child a ball of Play Dough and let them help mold the Play Dough around the bottle to form a mountain shape on the cookie sheet.
Let the children decorate and form the play dough if they wish. Make sure the whole jar is covered except for the opening at the top.
When the children are finished, spoon baking soda into the mouth of the jar (at least 1/3 of a cup).
To make the volcano erupt, slowly pour vinegar into the jar until it froths out.
You can make it erupt several times by pouring the vinegar again after each eruption subsides.