I love the jello-popcorn balls... However I am not sure how you would involve the kids in the making process (station wise) However you could make them up early and then have them wrapped in cling wrap and at that point let the kiddos decorate the wrapped ball. With a little cone hat and something for eyes, nose and a mouth. Or leave them unwrapped and hand each child a popcorn ball and let them put redhots on for eyes and nose (or conversation hearts) and a little piece of precut sting licorice for a mouth, then wrap it for them.
Good Luck
Colored Popcorn Balls
12 cups popped popcorn
1.5 oz flavored gelatin (any color Jello powder)
1/2 cup granulated sugar
1/2 cup light corn syrup
Put gelatin, sugar and syrup into a pot. Heat & stir to dissolve. Bring to a rolling boil. Pour over popcorn in a large bowl (you can lightly salt popcorn first if you like). Stir until all popcorn is coated. Form into balls with lightly buttered hands (I spray with Pam!). Makes about a dozen popcorn balls.
Use whatever color suits the occasion. For Halloween use orange Jello. You can put `faces' on your popcorn balls with candy. For Christmas make a bowl full of red & green balls. For Easter use pastel colors.