Heat chocolate-flavored candy coating according to package directions just until melted, stirring occasionally. Cool candy coating slightly. Meanwhile, inflate balloons to a 4-inch diameter. Carefully dip the balloons into the melted candy coating halfway up the balloon. (You want chocolate to coat balloon well to form a sturdy cauldron.) If desired, using a thin metal spatula, spread the chocolate coating to evenly coat the balloon. Place balloons on a parchment or waxed paper lined cookie sheet. Allow chocolate to run under bottom of balloon for support.
Place in the freezer for 20 to 30 minutes or until chocolate coating is very firm. Reserve any remaining chocolate coating to use for patching holes.
Working with one balloon at a time, prick balloon with a straight pin and deflate. Carefully remove balloon by gently pulling balloon away from the sides of the chocolate. Use a small brush to fill in any holes with remaining melted chocolate candy coating. Return to freezer.
Melt 2 ounces of the vanilla-flavored candy coating according to package directions. Cool candy coating. Working with one cauldron at a time, use a small brush to apply the melted candy coating to top edge of the cauldron, making drips down the sides. Chill in freezer to set. Melt the remaining vanilla candy coating. Tint melted candy coating with green food coloring. With a small brush, apply melted candy coating to the top edge of each cauldron, allowing coating to drip down the sides. Place in freezer to set.
Cauldrons can be stored in a covered container in the refrigerator for up to three days or in the freezer for up to one month. To assemble, scoop lime sherbet into the cauldrons. (Put cauldrons in freezer if not serving immediately.) Sprinkle with nonpareils and orange sugar and decorate with gummy worms right before serving.
Arrange pretzels on six serving plates to make campfires. If desired, circle pretzels with candy pebbles. Sprinkle with tinted coconut. Set cauldrons on top of pretzel campfires. Makes 6 servings.